Enter room dimensions to calculate paint needed. Dimensions up to 1000 ft, height up to 100 ft.
Paint Calculator: Paint Estimator, Painting Estimate Calculator, Paint Calculator Square Feet and the Complete Guide to Paint Coverage and Project Cost
Paint Calculator
Calculate how much paint you need for your room or project. Enter room dimensions, number of doors and windows, coats needed, and get an accurate estimate in gallons or quarts.
Learn More About Painting
Master painting techniques and prepare for your painting project:
Paint is one of the most accessible home improvement materials in the world — and one of the most consistently over-bought or under-bought. Walk into any decorating store and you will find people returning unused paint they over-ordered, or buying emergency top-up tins because they ran out halfway through the second coat. Both outcomes cost money and time that a reliable paint calculator prevents entirely. Whether you need a paint estimator to calculate litres or gallons for a single room, a painting estimate calculator to budget a full house repaint including materials and labour, or a paint calculator square feet approach to work out exactly how much paint covers a specific measured surface area — this guide provides every formula, every coverage rate, every surface adjustment, every product-type consideration, every labour cost benchmark, and every practical strategy for getting paint quantities and project costs right the first time, every time, for any surface worldwide.
Table of Contents
- Why the Paint Calculator Matters — The Real Cost of Getting It Wrong
- Paint Calculator — The Core Formula
- Paint Calculator Square Feet — US Coverage Reference Tables
- Paint Calculator — Metric Coverage Reference Tables (Litres per m²)
- Paint Estimator — Room-by-Room Calculation Method
- Paint Estimator — Deducting Doors and Windows
- Number of Coats — How Many Does Your Project Need?
- Paint Calculator for Ceilings
- Paint Calculator for Trim, Skirting and Woodwork
- Paint Type and Coverage — How Product Choice Affects Quantity
- Surface Condition and Porosity — How They Change Your Paint Estimate
- Painting Estimate Calculator — Full Room Budget
- Painting Estimate Calculator — Full House Interior
- Exterior Paint Calculator — Walls, Fascias and Masonry
- Paint Calculator for Specific Surfaces — Doors, Fences, Decks
- Global Paint Coverage Standards and Product Types
- After Effects — What Happens When Paint Quantities Are Miscalculated
- Paint Calculator Action Framework
- Frequently Asked Questions
1. Why the Paint Calculator Matters — The Real Cost of Getting It Wrong
Paint buying decisions are made in a context of uncertainty — most homeowners and even many tradespeople rely on rough estimates, the advice of a paint store assistant, or intuition about how much a room "looks like" it needs. The result is a structurally predictable set of errors that the paint calculator and paint estimator tools in this guide eliminate completely.
The Cost of Paint Miscalculation
| Error Type | What Happens | Financial Consequence |
|---|---|---|
| Buying too much paint | Leftover tins — storage problem — unused material — custom colours cannot be returned | Typically 15–30% cost waste — custom-tinted paint has zero resale or return value |
| Buying too little paint | Run out during final coat — visible lap lines between paint sessions — colour batch variation | Emergency purchase at full price — potential full repaint if colour batch differs — labour wasted |
| Wrong paint type for surface | Adhesion failure — peeling — cracking — wrong sheen for the environment | Full strip and repaint — typically 2–4× the original project cost |
| Under-specifying coat count | Insufficient opacity — dark colour showing through — uneven finish | Additional paint and labour to apply extra coat — potential full repaint |
| Not accounting for surface porosity | First coat absorbed into bare plaster or new drywall — leaves nothing on surface | Primer coat not planned — extra quantity needed — project delay |
| Batch/dye lot variation from separate purchases | Subtle colour difference between tins from different production runs | Repaint of entire feature wall or room — visible colour change at join |
2. Paint Calculator — The Core Formula
The paint calculator applies one fundamental formula: divide the surface area to be painted by the coverage rate of the paint, then multiply by the number of coats required.
Paint Calculator Formula
Paint Volume = (Surface Area ÷ Coverage Rate per Coat) × Number of Coats
Where:
Surface Area = total paintable area in m² or ft²
Coverage Rate = how many m² or ft² one litre/gallon covers (from product label)
Number of Coats = typically 2 for most interior applications, more for dark colours or porous surfaces
Metric Worked Example — Bedroom walls:
Room perimeter = (4m + 3m) × 2 = 14m
Wall height = 2.4m
Total wall area = 14m × 2.4m = 33.6 m²
Minus two doors (2m × 0.8m each) = 3.2 m²
Net paintable area = 33.6 − 3.2 = 30.4 m²
Coverage rate = 12 m² per litre (standard emulsion)
Coats = 2
Paint required = (30.4 ÷ 12) × 2 = 2.53 × 2 = 5.07 litres → buy 5.5 or 6 litres
Imperial Worked Example — 12ft × 14ft room:
Wall perimeter = (12 + 14) × 2 = 52 linear feet
Wall height = 8ft
Total wall area = 52 × 8 = 416 ft²
Minus two doors (80 × 32 inches each) ≈ 35.5 ft² each = 71 ft² total
Net paintable area = 416 − 71 = 345 ft²
Coverage rate = 400 ft² per gallon (standard interior paint)
Coats = 2
Paint required = (345 ÷ 400) × 2 = 0.86 × 2 = 1.72 gallons → buy 2 gallons
Coverage Rate Terminology
| Term | Metric | Imperial (US) | How It Appears on Product Labels |
|---|---|---|---|
| Coverage rate | m² per litre | ft² per gallon | "Covers approximately 12 m² per litre" or "covers up to 400 sq ft per gallon" |
| Spreading rate | m²/L | ft²/gal | Appears in product data sheets as "theoretical spreading rate" |
| Practical coverage | Typically 80–85% of stated rate | Stated coverage assumes perfect conditions | Real-world use generally 80–85% of label figure — allow for this |
3. Paint Calculator Square Feet — US Coverage Reference Tables
The paint calculator square feet approach is standard in the United States and Canada. Coverage is expressed in square feet per gallon, and paint is sold in quarts (0.25 gallon), 1-gallon, and 5-gallon containers. The following tables use 400 ft² per gallon as the standard baseline — the typical stated coverage for premium interior latex paint.
Paint Calculator Square Feet — Gallons Required by Area and Coats
| Surface Area (ft²) | 1 Coat (400 ft²/gal) | 2 Coats | 3 Coats | Practical Purchase |
|---|---|---|---|---|
| 100 ft² | 0.25 gal | 0.50 gal | 0.75 gal | 1 quart for 1–2 coats |
| 200 ft² | 0.50 gal | 1.00 gal | 1.50 gal | 1 gallon for 2 coats |
| 300 ft² | 0.75 gal | 1.50 gal | 2.25 gal | 2 gallons for 2 coats |
| 400 ft² | 1.00 gal | 2.00 gal | 3.00 gal | 2 gallons for 2 coats |
| 500 ft² | 1.25 gal | 2.50 gal | 3.75 gal | 3 gallons for 2 coats |
| 600 ft² | 1.50 gal | 3.00 gal | 4.50 gal | 3 gallons for 2 coats |
| 800 ft² | 2.00 gal | 4.00 gal | 6.00 gal | 4 gallons for 2 coats |
| 1,000 ft² | 2.50 gal | 5.00 gal | 7.50 gal | 5 gallons for 2 coats (1 × 5-gal bucket) |
| 1,200 ft² | 3.00 gal | 6.00 gal | 9.00 gal | 6 gallons for 2 coats |
| 1,500 ft² | 3.75 gal | 7.50 gal | 11.25 gal | 8 gallons for 2 coats |
| 2,000 ft² | 5.00 gal | 10.00 gal | 15.00 gal | 2 × 5-gal buckets for 2 coats |
Paint Calculator Square Feet — Standard Room Sizes (US)
| Room Type | Typical Dimensions | Wall Area (ft²) | Gallons (2 coats, walls only) |
|---|---|---|---|
| Small bathroom | 6 × 8 ft, 8 ft ceiling | ~180 ft² (less fixtures) | ~1 gallon |
| Average bedroom | 12 × 12 ft, 8 ft ceiling | ~310 ft² (less doors/windows) | ~2 gallons |
| Large bedroom / master | 14 × 16 ft, 9 ft ceiling | ~490 ft² | ~3 gallons |
| Average living room | 16 × 18 ft, 9 ft ceiling | ~570 ft² | ~3 gallons |
| Large living room / open plan | 20 × 24 ft, 9 ft ceiling | ~740 ft² | ~4 gallons |
| Kitchen | 12 × 14 ft, 9 ft ceiling | ~330 ft² (less cabinets) | ~2 gallons |
| Whole house interior (3 bed) | ~1,400–1,800 ft² floor area | ~2,000–2,600 ft² wall area | ~12–16 gallons |
4. Paint Calculator — Metric Coverage Reference Tables (Litres per m²)
The paint calculator in metric uses litres per litre of coverage — the standard for UK, Europe, Australia, India, and most of the world. Coverage rates on UK/EU products are typically stated as m² per litre, ranging from 10 m²/L (thick masonry paint) to 16 m²/L (thin primers on smooth surfaces).
Paint Calculator — Litres Required by Area and Coats (12 m²/L standard coverage)
| Surface Area (m²) | 1 Coat (12 m²/L) | 2 Coats | 3 Coats | Practical Purchase |
|---|---|---|---|---|
| 10 m² | 0.83 L | 1.67 L | 2.50 L | 2.5L tin for 2 coats |
| 15 m² | 1.25 L | 2.50 L | 3.75 L | 2.5L tin for 2 coats |
| 20 m² | 1.67 L | 3.33 L | 5.00 L | 5L tin for 2 coats |
| 25 m² | 2.08 L | 4.17 L | 6.25 L | 5L tin for 2 coats (tight) |
| 30 m² | 2.50 L | 5.00 L | 7.50 L | 5L tin for 2 coats |
| 40 m² | 3.33 L | 6.67 L | 10.00 L | 5L + 2.5L for 2 coats |
| 50 m² | 4.17 L | 8.33 L | 12.50 L | 10L (2 × 5L) for 2 coats |
| 60 m² | 5.00 L | 10.00 L | 15.00 L | 2 × 5L for 2 coats |
| 80 m² | 6.67 L | 13.33 L | 20.00 L | 3 × 5L for 2 coats |
| 100 m² | 8.33 L | 16.67 L | 25.00 L | 15L (3 × 5L) + 2.5L for 2 coats |
| 150 m² | 12.50 L | 25.00 L | 37.50 L | 5 × 5L for 2 coats |
Paint Calculator — Coverage Rates by Paint Type (Metric)
| Paint Type | Typical Coverage (m²/litre) |
|---|---|
| Matt emulsion (standard interior wall) | 10–14 m²/L |
| Silk emulsion (mid-sheen interior) | 10–13 m²/L |
| Eggshell (kitchen, bathroom, woodwork) | 12–15 m²/L |
| Satinwood (wood and trim) | 12–14 m²/L |
| Gloss (wood, metal) | 15–18 m²/L |
| Masonry paint (exterior) | 5–8 m²/L (highly porous surface) |
| Primer / undercoat (wood) | 10–14 m²/L |
| Primer (bare plaster / new walls) | 10–15 m²/L |
| Textured / sandpaper finish paint | 3–6 m²/L (high film build) |
| Floor paint (hard-wearing) | 8–12 m²/L |
5. Paint Estimator — Room-by-Room Calculation Method
The paint estimator breaks the total calculation into its component surfaces — walls, ceiling, and trim — calculating each separately because they may use different paint types, different coverage rates, and may require different numbers of coats. This is the most accurate approach for any room-level painting estimate calculator.
Paint Estimator — Step-by-Step Room Calculation
| Step | Action | Example (4m × 3.5m room, 2.4m ceiling) |
|---|---|---|
| 1 | Calculate wall perimeter | (4 + 3.5) × 2 = 15m perimeter |
| 2 | Calculate gross wall area | 15m × 2.4m = 36.0 m² |
| 3 | Deduct doors (standard = 2m × 0.8m) | 1 door = 1.6 m² → 36.0 − 1.6 = 34.4 m² |
| 4 | Deduct windows (standard = 1.2m × 1.0m) | 1 window = 1.2 m² → 34.4 − 1.2 = 33.2 m² |
| 5 | Divide by coverage rate per litre | 33.2 ÷ 12 = 2.77 litres per coat |
| 6 | Multiply by number of coats | 2.77 × 2 coats = 5.53 litres |
| 7 | Add 10% contingency | 5.53 × 1.10 = 6.08 litres → buy 2 × 2.5L + 1 × 1L tins |
Paint Estimator — Standard UK Room Paint Requirements Summary
| Room Size | Approx. Wall Area (m²) | Litres Required (2 coats, 12 m²/L) | Recommended Purchase |
|---|---|---|---|
| Small bedroom (3m × 3m, 2.4m ceiling) | ~28 m² | ~4.7 L | 5L tin |
| Standard bedroom (4m × 3m, 2.4m ceiling) | ~32 m² | ~5.3 L | 5L + 1L or 2 × 2.5L |
| Large bedroom (4.5m × 3.5m, 2.4m ceiling) | ~38 m² | ~6.3 L | 5L + 2.5L |
| Living room (5m × 4m, 2.4m ceiling) | ~50 m² | ~8.3 L | 2 × 5L (tight) or 10L |
| Large living room (6m × 4.5m, 2.4m ceiling) | ~60 m² | ~10.0 L | 2 × 5L |
| Kitchen (4m × 3m, 2.4m ceiling, cabinets deducted) | ~22 m² | ~3.7 L | 5L tin |
| Bathroom (2.5m × 2m, 2.4m ceiling) | ~18 m² | ~3.0 L | 2.5L + 1L or 5L (with ceiling) |
6. Paint Estimator — Deducting Doors and Windows
Every accurate paint estimator deducts the area of doors and windows from the gross wall area — because these are surfaces not painted with wall paint. Failure to deduct them produces a systematic over-order that is especially significant in rooms with large windows, French doors, or bifold openings.
Standard Door and Window Areas for Paint Estimator Deduction
| Opening Type | Standard Size (m) | Area to Deduct (m²) |
|---|---|---|
| Standard interior door | 2.0m × 0.8m | 1.6 m² |
| Wide interior door | 2.0m × 0.9m | 1.8 m² |
| Standard exterior door | 2.1m × 0.9m | 1.9 m² |
| Double door / French door | 2.1m × 1.8m | 3.8 m² |
| Bifold / sliding door (4-panel) | 2.1m × 2.4m | 5.0 m² |
| Small window | 0.9m × 0.9m | 0.8 m² |
| Standard window | 1.2m × 1.0m | 1.2 m² |
| Large window / bay section | 1.5m × 1.2m | 1.8 m² |
| Sash window (full height) | 1.2m × 1.5m | 1.8 m² |
| Floor-to-ceiling window/door | 2.4m × 1.8m | 4.3 m² |
When NOT to Deduct — The Trade Rule
Many professional painters do not deduct small windows and single doors when calculating paint quantities for the following practical reason: the paint "saved" by not painting the door or window is offset by the extra paint used on cutting-in around the frame, on wastage from tray charging, and from the unavoidable extra passes around window reveals. As a general rule, professional estimators deduct only openings larger than 2 m² — deducting smaller openings produces false precision without meaningful quantity savings. For a painting estimate calculator aimed at general accuracy, deducting only doors (1.6–1.9 m²) and windows over 1 m² is a reasonable professional practice.
7. Number of Coats — How Many Does Your Project Need?
The number of coats required is the second most important input in any paint calculator — and the most commonly underestimated. Specifying too few coats saves paint in the estimate but results in poor opacity, visible brush marks, or colour showing through — requiring an additional coat anyway, at full cost but with the inconvenience of the project running longer than planned.
Recommended Coat Count by Situation
| Situation | Recommended Coats | Notes |
|---|---|---|
| Repaint same or similar colour (wall to wall) | 1–2 coats | High-quality paint on good surfaces may achieve good coverage in 1 coat — always check before second coat |
| Repaint light colour over light colour | 2 coats | Standard — allows for any imperfections in first coat to be fully covered |
| Dark colour over light (or light over dark) | 2–3 coats | Dark-to-light almost always 3 coats minimum — light-to-dark 2–3 depending on pigment load |
| Bold or deep colour (red, dark navy, deep green) | 3 coats (some colours: 4) | Reds and oranges are notoriously low-hide pigments — plan for 3 coats minimum |
| New plaster (properly primed) | 1 mist coat + 2 coats | Mist coat seals bare plaster — then 2 standard coats |
| New drywall (plasterboard) | 1 primer + 2 coats | Must prime drywall before topcoat — joint compound absorbs paint differently |
| Wood — bare | 1 primer + 2 coats topcoat | Knotting compound over resinous knots before primer |
| Previously painted wood in good condition | 1–2 coats topcoat | Sand lightly first — 1 coat if same colour, 2 if changing |
| Metal (bare) | 1 metal primer + 1–2 topcoats | Rust-inhibiting primer essential on bare metal |
| Exterior masonry (previously painted, good condition) | 2 coats | Stabilising primer if powdery or loose — otherwise 2 coats masonry paint |
| Exterior masonry (bare or new render) | 1 stabiliser + 2–3 coats masonry paint | Highly porous — expect significantly higher consumption than stated coverage rate |
8. Paint Calculator for Ceilings
Ceilings are often omitted from initial paint calculator estimates but represent a significant separate quantity — especially for high-quality ceiling paint which is typically a different product from wall paint. Ceiling paint is usually sold as a flat/matt finish and covers at a similar rate to wall emulsion.
Paint Calculator — Ceiling Area and Litres Required
| Room Dimensions (floor area) | Ceiling Area (m²) | Litres Required (2 coats, 12 m²/L) | Practical Purchase |
|---|---|---|---|
| 2.5m × 2.0m (small bathroom) | 5.0 m² | 0.83 L | 1L tin |
| 3.0m × 3.0m (small bedroom) | 9.0 m² | 1.50 L | 2.5L tin (shares with walls) |
| 4.0m × 3.0m (standard bedroom) | 12.0 m² | 2.00 L | 2.5L tin |
| 5.0m × 4.0m (living room) | 20.0 m² | 3.33 L | 5L tin (some left over) |
| 6.0m × 5.0m (large living room) | 30.0 m² | 5.00 L | 5L tin exactly |
| 8.0m × 5.0m (open plan) | 40.0 m² | 6.67 L | 5L + 2.5L |
9. Paint Calculator for Trim, Skirting and Woodwork
Trim painting — skirting boards, architraves, door frames, window frames, and dado rails — is calculated separately in any accurate paint estimator because it uses different paint (typically gloss, satinwood, or eggshell) and has a different coverage rate. Woodwork paint is sold in smaller quantities — 750ml, 1L, and 2.5L tins — and covers at a higher rate than emulsion (15–18 m²/L for gloss).
Woodwork and Trim Paint Calculator — Linear Metre Reference
| Trim Type | Typical Width | m² per linear metre |
|---|---|---|
| Skirting board (standard) | 100mm | 0.10 m²/lm |
| Skirting board (tall) | 150mm | 0.15 m²/lm |
| Door architrave | 60–70mm | 0.065 m²/lm |
| Dado rail | 60–80mm | 0.07 m²/lm |
| Coving / cornice | 100–125mm | 0.115 m²/lm |
Paint Estimator — Woodwork Litres for a Standard Room
| Room Type | Approx. Total Woodwork Area (m²) | Litres Required (2 coats, 16 m²/L gloss) |
|---|---|---|
| Small bedroom with skirting + 1 door | ~4–5 m² | ~0.6 L → 1 × 750ml tin |
| Standard bedroom with full trim + 1 door | ~6–8 m² | ~0.9 L → 1 × 1L tin |
| Living room with full trim + 2 doors + bay window | ~10–15 m² | ~1.5 L → 2 × 750ml or 1 × 2.5L |
| Full house interior (3 bed semi) | ~50–70 m² | ~6–9 L → 3–4 × 2.5L tins |
10. Paint Type and Coverage — How Product Choice Affects Quantity
The paint calculator result changes significantly depending on which paint product is chosen — even for the same surface. Premium paints with higher pigment loads cover more surface per litre in fewer coats, which may reduce the total volume required despite the higher price per litre. Budget paints with lower pigment content cover less per coat and may require an additional coat, offsetting the apparent price advantage.
Paint Quality vs Coverage — The True Cost Per m²
| Paint Tier | Coverage Rate | Price per 5L (UK est.) | Coats for Good Coverage | Cost per m² (materials only) |
|---|---|---|---|---|
| Budget emulsion | ~10 m²/L | ~£15–£25 | 3 coats (low hide) | ~£0.90–£1.50/m² |
| Mid-range emulsion | ~12 m²/L | ~£25–£40 | 2 coats | ~£0.83–£1.33/m² |
| Premium emulsion | ~14 m²/L | ~£40–£70 | 1–2 coats | ~£0.71–£1.25/m² |
| Professional trade emulsion | ~12–14 m²/L | ~£30–£55 | 2 coats (high hide) | ~£0.80–£1.15/m² |
A budget paint at £0.90/m² (3 coats) may appear cheaper than a premium at £1.25/m² (2 coats) — but the premium paint requires one fewer coat, saving a full day of labour time. For a professional decorator charging £150–£250/day, the labour saving from one fewer coat across a whole house project far exceeds the paint price premium. The painting estimate calculator must always integrate both material cost and labour cost to reveal the true project economy.
11. Surface Condition and Porosity — How They Change Your Paint Estimate
The label coverage rate assumes a smooth, sealed, previously painted surface in good condition. Real-world surfaces deviate from this ideal in ways that materially increase the paint required. Every paint estimator should adjust for surface condition before finalising quantities.
Surface Condition Adjustment Factors
| Surface Condition | Adjustment to Standard Coverage | Practical Implication |
|---|---|---|
| Smooth, sealed, good previously painted surface | 100% — use label coverage rate | Standard calculation applies directly |
| Slightly rough or textured (brushed plaster, light texture) | 80–90% of label rate | Add 10–20% to calculated quantity |
| New bare plaster (NOT primed) | 50–60% of label rate for first coat | Mist coat will be heavily absorbed — double quantity for first coat |
| New drywall / plasterboard (not primed) | 60–70% of label rate | Always prime before top-coating — joint compound areas absorb more |
| Bare exterior masonry / brick | 30–50% of label rate (heavy absorption) | Stabiliser first — plan for 3+ coats of masonry paint |
| Heavily textured wall (Artex, rough render) | 50–60% of label rate | Deeply textured surfaces absorb and trap paint — significantly higher consumption |
| Smooth, well-sanded bare wood | 70–80% of label rate (first coat) | Primer required — subsequent coats at standard rate after sealing |
12. Painting Estimate Calculator — Full Room Budget
The painting estimate calculator for a complete room budget adds labour cost to material cost — producing the full picture of what a painting project will cost if professionally executed or helping a DIY painter understand what they are saving by doing it themselves.
Painting Estimate Calculator — Standard Bedroom (UK, Professional Decorator)
| Cost Element | Specification | Estimated Cost |
|---|---|---|
| Wall paint — 2 coats | 5L tin mid-range emulsion | £25–£40 |
| Ceiling paint — 2 coats | 2.5L ceiling white | £15–£25 |
| Woodwork paint — 2 coats | 1L satinwood | £12–£20 |
| Primer / mist coat (if needed) | 1L PVA or diluted emulsion | £5–£15 |
| Sundries (tape, dust sheets, brush/roller set, tray) | Consumables | £15–£30 |
| Labour — professional decorator | 1.5–2 days at £150–£250/day | £225–£500 |
| Total — standard bedroom (professionally decorated) | £297–£630 | |
| DIY total (materials only) | £72–£130 |
13. Painting Estimate Calculator — Full House Interior
The painting estimate calculator for a complete interior repaint of a typical 3-bedroom house is one of the most commonly requested estimates in home improvement. The total cost varies enormously by quality of finish, paint brand, and whether professional decorating labour is used.
Painting Estimate Calculator — 3-Bedroom House Interior (UK 2024–2025)
| Area | Total Wall Area (est.) | Paint Quantity (2 coats) | Material Cost (mid-range) | Professional Labour |
|---|---|---|---|---|
| 3 bedrooms | ~100 m² | ~17 L emulsion | £80–£130 | £300–£600 |
| Living room / dining | ~55 m² | ~9 L emulsion | £45–£80 | £200–£400 |
| Kitchen | ~25 m² | ~4 L eggshell | £30–£60 | £150–£250 |
| Bathrooms (×2) | ~30 m² | ~5 L moisture-resistant | £35–£65 | £150–£280 |
| Hallway / landing / stairs | ~40 m² | ~7 L emulsion | £35–£60 | £200–£400 |
| Ceilings throughout | ~85 m² (floor area) | ~14 L ceiling white | £50–£90 | £300–£500 |
| All woodwork (skirting, doors, frames) | ~60 m² woodwork | ~7 L satinwood/gloss | £50–£100 | £350–£700 |
| Full house total | ~63 L total paint | ~£325–£585 | £1,650–£3,130 | |
| Total project cost (materials + labour) | £1,975–£3,715 |
Professional Decorator Day Rates — International Reference
| Country | Typical Day Rate (Professional Decorator) | Typical m² Rate (Walls, painted) |
|---|---|---|
| United Kingdom | £150–£250/day | £6–£12/m² |
| United States | $200–$450/day | $1.50–$4.00/ft² ($16–$43/m²) |
| Australia | AUD $300–$600/day | AUD $15–$25/m² |
| Canada | CAD $250–$500/day | CAD $1.50–$3.50/ft² |
| Germany | €200–€350/day | €12–€20/m² |
| India | ₹800–₹2,000/day | ₹15–₹35/ft² |
| UAE | AED 200–450/day | AED 4–10/ft² |
| Singapore | SGD $250–$500/day | SGD $1.50–$3/ft² |
14. Exterior Paint Calculator — Walls, Fascias and Masonry
The exterior paint calculator follows the same formula as interior but with critical differences: exterior masonry paints have much lower coverage rates (5–8 m²/L vs 12–14 for interior), exterior surfaces are significantly more porous and uneven, and the number of coats is typically higher. The paint estimator for an exterior project must also account for the surface area of fascias, soffits, and any exposed woodwork.
Exterior Paint Calculator — Masonry Wall Coverage
| House Type | Approx. Masonry Area (m²) | Litres Required (2 coats, 6 m²/L masonry) | Stabiliser First? |
|---|---|---|---|
| Small terraced house | ~60–80 m² (one front elevation) | ~20–27 L | If powdery or bare: yes |
| Semi-detached house (2 sides) | ~120–160 m² | ~40–54 L | Condition-dependent |
| Detached house (all sides) | ~200–280 m² | ~67–93 L | Condition-dependent |
| Large detached / farmhouse | ~300–500 m² | ~100–167 L | Usually required |
15. Paint Calculator for Specific Surfaces — Doors, Fences and Decks
Paint Calculator — Specific Surfaces Quick Reference
| Surface | Typical Area | Paint Type | Coverage Rate | Litres for 2 Coats |
|---|---|---|---|---|
| Standard interior door (both sides) | ~3.2 m² | Gloss or satinwood | 16 m²/L | ~0.4 L → 1 × 500ml tin |
| Panel front door (exterior, both sides) | ~4 m² | Exterior gloss/eggshell | 14 m²/L | ~0.6 L → 750ml tin |
| Garden fence (1m × 10m = 10 m²) | 10 m² one side | Fence stain or paint | 5–7 m²/L (rough wood) | ~3 L for 2 coats |
| Garden fence (1m × 20m = 20 m²) | 20 m² one side | Fence stain or paint | 5–7 m²/L | ~6 L for 2 coats |
| Decking (4m × 3m = 12 m²) | 12 m² | Decking oil/stain | 4–6 m²/L (bare wood) | ~4–6 L for 2 coats |
| Shed exterior (medium shed) | ~20–25 m² | Exterior wood paint or preservative | 6–10 m²/L | ~5–8 L for 2 coats |
| Garage door (large roller or double) | ~8–12 m² | Metal or gloss exterior | 12–15 m²/L | ~1.2–2.0 L for 2 coats |
16. Global Paint Coverage Standards and Product Types
Paint products, coverage rates, and sheen terminology differ by country. The paint calculator square feet approach is standard in the US; litres-per-m² in the UK, EU, and Australia. Understanding these differences prevents errors when buying imported brands or working from foreign specifications.
Paint Sheen Terminology by Market
| Sheen Level | UK Term | US Term | Australia Term | Typical Use |
|---|---|---|---|---|
| Least sheen | Matt / flat | Flat / matte | Flat | Ceilings, feature walls, low-traffic rooms |
| Low sheen | Soft sheen / velvet | Eggshell | Low sheen | General living areas — wipeable |
| Mid sheen | Silk / satin | Satin | Semi-gloss (sometimes) | Hallways, children's rooms, kitchens |
| Higher sheen (wood/trim) | Eggshell / satinwood | Semi-gloss | Semi-gloss | Trim, skirting, doors, woodwork |
| Full gloss | Gloss | High-gloss | Gloss | High-wear woodwork, exterior metalwork |
17. After Effects — What Happens When Paint Quantities Are Miscalculated
The consequences of paint quantity errors are not merely aesthetic — they involve real financial costs, project delays, and in some cases permanent quality deficiencies that cannot be corrected without repainting the entire surface.
After Effects of Running Out of Paint Mid-Project
The dye lot problem — when buying more later costs more than paint: Paint, like fabric, is produced in batches. Each production batch of a tinted colour has its own dye lot — a slight natural variation in the mix that produces a colour imperceptibly different from the previous batch. On a wall or ceiling, this difference is invisible within a single batch. Between batches, it becomes visible — especially in raking light — as a subtle shift in colour across the join between the area painted with the original tin and the area repainted with the new batch. The industry-standard solution is to buy all the paint needed for a single surface from the same batch at the same time. Custom-tinted paints (any non-standard colour) are particularly vulnerable because the mixing machine parameters can shift between tints. Running out and buying more is not just a cost problem — it is a colour consistency problem that may force a full repaint of the affected area to achieve an even result. The paint calculator used correctly before purchase eliminates this risk entirely.
The emergency premium purchase: Running short during a professional decorating job — with a decorator standing idle while someone runs to the paint shop — costs both the material price and the wasted labour time. A decorator charging £200/day for a job estimated at 1.5 days may charge the full 2 days if a mid-project shortage creates a waiting period. The extra 2.5 litres of paint that would have prevented the shortfall might cost £15. The wasted labour time costs £100 or more. The paint estimator that correctly calculates quantities with a 10% contingency is a cash-flow protection tool, not just a shopping list.
After Effects of Wrong Paint Type
The bathroom wall mould problem — using the wrong paint in wet areas: Standard interior matt emulsion absorbs moisture — making it entirely unsuitable for bathroom walls, steam-prone kitchen areas, or any surface that regularly reaches high humidity. A bathroom painted with standard emulsion will begin to show condensation marks within months, black mould growth along the ceiling line and behind shower areas within 12–18 months, and progressive paint failure (blistering, peeling) within 2–3 years. The correct product — a moisture-resistant or bathroom-specific paint with a low-permeability binder — costs approximately the same or slightly more than standard emulsion. The stripping, preparation, and repainting required to remediate a bathroom that was painted with the wrong product costs a full repaint plus any mould treatment — typically 3–5× the original project cost. The painting estimate calculator that specifies bathroom-appropriate paint prevents this entirely.
Painting over oil-based paint with water-based without priming — the adhesion failure: Modern water-based paints have excellent adhesion properties — but they do not reliably bond to a surface coated with old oil-based gloss without preparation. Painting water-based eggshell over old oil-based gloss without sanding or applying a bonding primer creates adhesion failure: the topcoat may appear fine for weeks but will eventually peel in sheets — typically triggered by temperature change, cleaning, or physical impact. The only remedy is to strip the failed paint back, sand the old gloss, apply a bonding primer, and repaint — a project that takes 3–4× the time and cost of the original. A painting estimate calculator that correctly identifies the existing paint type and specifies the appropriate preparation sequence prevents this structural failure.
After Effects of Insufficient Coats
The bold colour bleed-through — the red paint trap: Red, orange, and certain deep earth tones are notoriously difficult pigments — they have low hiding power because the pigment molecules themselves have low opacity. Applying two coats of a bold red over a pale wall often produces visible pale patches where the underlying colour shows through, particularly in corners and at roller reversal lines. The instinct is to apply a third coat — but a patchy, two-coat surface will often show lap lines and texture variation through the third coat if the second coat was applied too thinly or at the wrong consistency. The correct approach, identified before starting, is to: use a grey primer as a mid-tone base, accept from the outset that bold colours require 3 minimum coats, and use a higher-quality paint with better pigment load. An accurate paint estimator that specifies 3 coats for bold colours prevents the need for emergency extra material after a disappointing 2-coat result.
18. Paint Calculator Action Framework
| Step | Action | Reference |
|---|---|---|
| 1 | Measure all surfaces — room by room — length × height for each wall | Use tape measure — record in same units throughout |
| 2 | Calculate gross wall area (perimeter × ceiling height) | Section 2 — core formula |
| 3 | Deduct doors and windows (openings over 1 m²) | Section 6 — standard opening areas table |
| 4 | Identify paint type needed for each surface — check moisture, surface condition | Section 10 — paint type coverage rates table |
| 5 | Determine number of coats — consider existing colour, surface porosity, bold colours | Section 7 — coat count by situation |
| 6 | Adjust for surface condition (bare plaster, textured surface, exterior masonry) | Section 11 — surface condition adjustment table |
| 7 | Apply paint calculator formula: (Area ÷ Coverage) × Coats | Section 2 — worked metric and imperial examples |
| 8 | Add 10% contingency — then round up to nearest available tin size | Always buy slightly more — return is easier than running short |
| 9 | Calculate ceiling and woodwork separately at different coverage rates | Section 8 (ceilings) and Section 9 (woodwork) |
| 10 | Run painting estimate calculator — add labour at day rate for total project cost | Section 12–13 — full room and house cost tables |
19. Frequently Asked Questions
How does a paint calculator work?
A paint calculator divides the total paintable surface area by the coverage rate of the paint (in m² per litre or ft² per gallon), then multiplies by the number of coats. The surface area is calculated as wall perimeter × height (for rooms) or length × width (for single walls, ceilings, or flat surfaces), minus any deductions for doors, windows, or other non-painted openings. The result gives the minimum volume needed — add 10% contingency and round up to the nearest available tin size.
How do I use a paint calculator in square feet?
The paint calculator square feet method is identical in principle to the metric approach but uses US units. Measure each wall in feet (length and height), multiply to get area in square feet, sum all walls, deduct doors and windows, then divide by the paint's coverage rate (typically 350–400 ft² per gallon for standard interior paint). Multiply by number of coats and add 10%. Paint in the US is sold in quarts (0.25 gallon), 1-gallon, and 5-gallon containers — round up to the nearest size that covers the calculated volume.
How many litres of paint do I need for a room?
For a standard bedroom (approximately 4m × 3m with 2.4m ceilings), using a mid-range emulsion at 12 m²/L coverage: wall area ≈ 32 m² (after deducting one door and one window); divided by 12 = 2.67 L per coat; two coats = 5.33 L + 10% = 5.87 L. Buy a 5L tin and a 1L tin, or two 2.5L tins. Ceiling: 4 × 3 = 12 m²; divided by 12 = 1.0 L per coat; two coats = 2.0 L + 10% = 2.2 L → buy one 2.5L ceiling paint tin.
What is a paint estimator and how accurate is it?
A paint estimator calculates paint quantities from surface measurements and product specifications. Accuracy depends on four factors: the accuracy of the measurements (measure twice), the accuracy of the coverage rate used (use the actual label figure rather than a generic assumption), the correct coat count for the situation (see Section 7), and whether surface condition adjustments are applied (bare plaster or textured walls consume significantly more paint than stated label rates on smooth surfaces). A properly applied paint estimator is accurate to within 5–10% — meaning the 10% contingency added to any estimate provides comfortable confidence that you will not run short.
Why does my paint not cover as well as the label says?
Paint labels state "theoretical spreading rate" — which is the coverage achievable under ideal laboratory conditions on a smooth, non-porous, horizontal surface. Real-world application always produces lower coverage due to: surface texture and porosity absorbing more paint; roller and brush wastage (paint left in the tray, on the roller core, on the brush); cut-in work around edges and corners that wastes paint; and the natural variation in how thickly each painter applies paint. Professionals typically achieve 80–85% of the stated rate. This is why the paint estimator in this guide uses 12 m²/L as the baseline rather than the often-stated 14–16 m²/L on premium paint labels — the real-world figure is conservative and produces a quantity that is sufficient rather than one that falls short.
This content is for educational and informational purposes only. All paint coverage rates are approximate and based on typical product specifications — actual coverage varies by specific product, surface condition, application method, and painter technique. Price estimates for paint and professional labour are indicative figures based on general UK and global market conditions in 2024–2025 and are subject to regional and seasonal variation — always obtain specific product data from the paint manufacturer's technical data sheet and current local quotes from suppliers and contractors. Coverage rates for specific products should always be taken from the product label or manufacturer's technical documentation rather than general averages. Nothing in this guide constitutes professional decorating advice for specific applications involving specialist coatings, heritage buildings, or commercial specifications.