How to Convert Between Metric and Imperial Measurements
Working across metric and imperial systems is unavoidable in construction. This guide explains the most important conversion factors, shows you how to apply them, and gives you practical shortcuts for common on-site calculations.
The Core Conversion Factors for Construction
Six conversion factors cover the vast majority of construction unit conversion needs. For length: 1 inch equals 2.54 centimeters, and 1 foot equals 0.3048 meters. For area: 1 square foot equals 0.0929 square meters. For volume: 1 cubic foot equals 0.0283 cubic meters, and 1 US gallon equals 3.785 liters. For mass: 1 pound equals 0.4536 kilograms.
The inverse relationships are equally useful. One meter equals 3.281 feet, 1 square meter equals 10.764 square feet, 1 cubic meter equals 35.315 cubic feet, 1 liter equals 0.264 US gallons, and 1 kilogram equals 2.205 pounds. Committing these twelve values to memory enables the majority of field conversions without reference materials.
For quick mental estimates, use rounded approximations: 1 meter is roughly 3.3 feet, 1 kilogram is roughly 2.2 pounds, and 1 liter is roughly a quarter gallon. These approximations introduce small errors (under 2 percent) but are adequate for planning and rough estimates when you do not need decimal precision.
Step 1 – Convert Length and Distance
To convert meters to feet, multiply by 3.281. For a room measured at 4.2 meters long: 4.2 times 3.281 equals 13.78 feet, or approximately 13 feet 9.4 inches. To express the decimal feet as inches, multiply the decimal portion (0.78) by 12: 0.78 times 12 equals 9.4 inches.
To convert feet to meters, multiply by 0.3048. For a doorway that is 6 feet 8 inches tall: first convert to decimal feet (6 plus 8/12 equals 6.667 feet), then multiply by 0.3048: 6.667 times 0.3048 equals 2.032 meters.
For millimeters, divide by 25.4 to get inches, or divide by 1000 to get meters. Technical drawings from European and international manufacturers often dimension in millimeters. A bolt hole specified as 12 mm is 12 divided by 25.4, or 0.472 inches — very close to a 15/32 inch hole or a standard 1/2 inch hole.
Step 2 – Convert Area
To convert square feet to square meters, multiply by 0.0929. A 1,500-square-foot house has 1,500 times 0.0929, or approximately 139.4 square meters. To convert in the other direction, multiply square meters by 10.764. A 200-square-meter commercial space is 200 times 10.764, or 2,152.8 square feet.
For tile and flooring materials sold in square meters (common with European imports), convert your room's square footage to square meters before determining how many boxes to buy. A 168-square-foot room requires 168 times 0.0929, or 15.6 square meters of flooring. Divide 15.6 by the coverage per box to find box quantity.
Area conversions compound the errors of length conversions. When converting a length measurement to meters and then calculating area, small length errors get squared. For critical area calculations, use a calculator with full precision rather than relying on mental math with rounded conversion factors.
Step 3 – Convert Volume and Weight
To convert cubic feet to cubic meters, multiply by 0.0283. One cubic yard (27 cubic feet) equals 27 times 0.0283, or 0.765 cubic meters. This conversion is relevant when ordering materials from suppliers that quote prices per cubic meter, which is common for concrete, gravel, and bulk fill in countries using the metric system.
For liquid volumes, 1 US gallon equals 3.785 liters. Coatings, sealers, and adhesives are sold in liters in most countries outside the United States. If a coverage rate is given as 8 square meters per liter and you need to cover 500 square feet (46.5 square meters), you need 46.5 divided by 8, or 5.8 liters, which equals 5.8 times 0.264, or approximately 1.5 gallons.
Weight conversions are important for structural calculations and material delivery. Reinforcing steel, concrete block, and structural lumber all have weight specifications that affect floor loading and delivery logistics. One kilogram equals 2.205 pounds. For a delivery of 500 kilograms of rebar: 500 times 2.205 equals 1,102.5 pounds, or about 0.55 tons.
Practical Shortcuts and Avoiding Common Mistakes
The most common mistake in unit conversion is forgetting to square or cube the conversion factor when converting area or volume. Converting a length of 3 feet to meters gives 0.914 meters. But converting 3 square feet to square meters is not 0.914 squared — you multiply 3 by 0.0929, giving 0.279 square meters. The length conversion factor and the area conversion factor are different values.
A reliable way to verify a conversion is to convert back. If you converted 5 meters to feet and got 16.4 feet, convert 16.4 feet back to meters: 16.4 times 0.3048 equals 4.999 meters, which rounds to 5 meters. If the round-trip conversion gets you back to the original value (within rounding precision), your conversion is correct.
For recurring conversions in a specific project context, create a quick reference sheet with the most frequently used values pre-converted. If a project uses 12 standard panel widths, calculate all of them once in both feet and meters and keep the reference on site. This eliminates repetitive calculation errors and keeps the team working in consistent units.