Metric-Imperial Converter

A conversion only matters at the moment two numbers on the same job are written in different systems. A supplier quotes decking in linear meters while the framing plan is dimensioned in feet, a tile box is labeled in square feet while the room was measured with a metric tape, or a mortar bag states kilograms while the mix table is written in pounds. Getting that single multiplication wrong does not produce a small error. It produces an order that is out by a factor of three, eleven or a thousand. The eight pairs on this page cover the four quantity types a home project is actually ordered in: length, area, liquid volume and mass.

Why a converted number is not a buyable quantity

Converting 10 square meters gives 107.6391 square feet, and no supplier sells 107.6391 of anything. The conversion is only the first of three steps. The second step adds whatever waste allowance the layout deserves, and the third divides the padded figure by the selling unit and rounds up to a whole pack. Suppose a flooring box covers 15 square feet and you carry a 10 percent allowance. The converted 107.6391 becomes 118.4 square feet, 118.4 divided by 15 is 7.9, and the order is 8 boxes rather than the 7.18 boxes the bare conversion suggests. Reading a converted number as an order quantity is how a job finishes one box short on the final row, which is exactly the row where a change of dye lot shows.

Source: National Institute of Standards and Technology, NIST Special Publication 1038: The International System of Units, Conversion Factors for General Use.

NIST SP 1038 prints exact conversion values in bold and rounds the remainder to seven significant digits. The gallon it tabulates is the US gallon of 128 fluid ounces, or 231 cubic inches.

Recording a measurement so it survives conversion

1. Write the unit beside every figure. Record each dimension in your notes with its unit attached, such as 3.6 m or 11 ft 10 in, before you leave the room. A bare number sitting in a takeoff column is the single most common reason a conversion later gets applied in the wrong direction. Tool: Steel tape or laser measure.
2. Collapse mixed feet and inches first. NIST advises converting a combined figure to the smaller unit before you change systems, so 12 feet 5 inches becomes 149 inches and 1 pound 3.5 ounces becomes 19.5 ounces. Feed that single number into the converter rather than the pair of numbers. Tool: Pocket calculator.
3. Measure the product, not the label. Check every nominal size against the piece in front of you. Stock sold as half inch should read 12.7 millimeters on a caliper, while a 12 millimeter panel reads 0.4724 inches, so the two are not substitutes even though the labels look close. Tool: Digital caliper or folding rule.
4. Pick the direction and read the named target. Choose the source-to-target pair you need, such as square metres to square feet. There is no second unit-system control on this converter. The result prints the selected target unit beside the number, so copy both the value and that unit into your project notes. Tool: Conversion selector.
5. Round once, at the end of the math. Carry the full converted figure through any area, volume or waste arithmetic that follows, and round only when you reach a quantity you will actually order. Rounding at each intermediate step compounds the drift straight into the pack count. Tool: Takeoff sheet.
6. Send the answer back the other way. Run the result through the opposite pair and compare it with your original measurement. Converting 107.6391 with ft2-m2 returns 9.9999996 square meters, which confirms both the direction of the conversion and the position of the decimal point. Tool: The same converter.

Ten square meters of floor turned into square feet

The room measured 4.0 meters by 2.5 meters, which is 10 square meters of floor. Choose square metres to square feet in the Conversion and source unit field, then enter 10. The tool multiplies by the stored factor of 10.76391 and prints 107.6391 square feet. The unrounded reciprocal of 0.09290304 would give 107.639104167, so the stored factor costs about four millionths of a square foot on this job. The same control offers eight explicit directions for length, area, liquid volume, and mass; each result names its target unit. Hold the rounding until the end: 107.6391 becomes 108 square feet only when a later ordering calculation requires a whole box.

Result: 107.6391 square feet.

Where the eight pairs in this tool come from

Four of the eight factors are exact by definition and four are arithmetic reciprocals of those exact values. The foot is defined as 0.3048 meters, the square foot as 0.09290304 square meters and the pound as 0.45359237 kilograms, all of which appear in the NIST conversion tables. The US gallon is defined as 231 cubic inches, and because one cubic inch is 16.387064 cubic centimeters, the gallon works out at 3785.411784 milliliters. Going the other way the tool divides one by those constants and stores the result rounded: 3.28084 for meters to feet, 10.76391 for square meters to square feet, 2.20462262 for kilograms to pounds and 0.264172052 for liters to US gallons. That rounding sits far below anything a tape measure can resolve. Across a 1000 meter run the stored meters to feet factor differs from the unrounded reciprocal by about 0.0001 feet, which is roughly one thousandth of an inch.

Nominal metric sizes are not exact inch equivalents

Sheet goods and framing are where the two systems drift apart in a way arithmetic cannot repair. A 4 foot by 8 foot sheet is 32 square feet, which converts to 2.97289728 square meters, while a 1200 by 2400 millimeter sheet covers 2.88 square meters. The metric sheet is about 3.1 percent smaller, so a takeoff that treats the two as interchangeable comes up short by roughly one sheet in every 32. Stud and joist spacing behaves the same way. Framing at 16 inches on center is 406.4 millimeters, a 400 millimeter metric layout is 15.748 inches, and 24 inches is 609.6 millimeters against a nominal 600 millimeters. A 12 millimeter panel measures 0.4724 inches, not the 12.7 millimeters that a half inch board actually reads on a caliper. Convert the dimension you measured, never the size printed on the label.

Common mistakes

Running the conversion in the wrong direction because the pair name was read too quickly.

The m2-ft2 and ft2-m2 entries sit next to each other in the list and their factors differ by about 116 times, so a reversed pair turns a 10 square meter room into 0.929 square meters instead of 107.6391 square feet. Sanity check the answer before you use it. A square meter figure converted to square feet should grow roughly elevenfold, and the reverse conversion should shrink by the same amount.

Treating a nominal metric size as the exact equivalent of the inch size it replaced.

A 1200 by 2400 millimeter sheet covers 2.88 square meters while a 4 by 8 foot sheet covers 2.97289728 square meters, a shortfall of about 3.1 percent that the converter cannot see because the sheet itself was never measured. Convert the dimension taken off the real product rather than the size printed on the label, then rebuild the sheet count from that converted area.

Rounding the converted figure at every intermediate step of a takeoff.

NIST guidance is to keep all digits through the arithmetic and round once at the end, because repeated rounding drifts the total and the drift always lands in the pack count you finally order. Store the full converted number in the takeoff row and apply a single rounding rule at the point the quantity becomes an order, not before.

Rounding a clearance or a minimum dimension the way you round a material quantity.

NIST points out that 10 feet of electrical clearance rounds to 3 meters for general use but must be stated as 3.05 meters in a safety code, since 3 meters is a smaller gap than the rule demands. Round a limit in the direction that keeps the original rule intact, which means rounding a minimum up and a maximum down, and keep the untouched figure written beside it.

Assuming the gallon on a foreign data sheet is the same gallon this tool converts.

NIST SP 1038 warns that some inch pound unit names were also used in other countries for units of a different magnitude, and defines the gallon it tabulates as 128 fluid ounces, or 231 cubic inches. Confirm the sheet means the US gallon of 231 cubic inches before you use the gal-l or l-gal pair, and work from the stated milliliter figure whenever the sheet gives one.

Rounding without breaking a clearance or a limit

NIST guidance is blunt about the order of operations: keep every digit through the arithmetic and round once, at the end. How many digits you keep depends on the original measurement. If the first significant digit of the converted value is greater than or equal to the first digit of the original, keep the same count of significant digits, so 60.5 miles becomes 97.4 kilometers. If the converted value starts with a smaller digit, keep one more, so 8 feet becomes 2.4 meters rather than 2 meters. Where the original figure is a legal maximum or minimum, the rounding has to move in the safe direction. NIST gives the case of a 10 foot electrical clearance, which rounds to 3 meters for general use but has to be written as 3.05 meters in a safety code, because 3 meters would quietly shrink the required gap.

Frequently asked questions

How does the result identify its target unit?

The selected pair carries both direction and unit. Choosing square metres to square feet prints the answer as square feet, while choosing US gallons to litres prints litres. The target name appears next to every result instead of a neutral converted-units label. Copy that unit with the number so a later calculation cannot mistake an area for a length or apply the same conversion twice.

Is there a separate Metric or Imperial control?

This converter has no separate Metric or Imperial selector. Choose one of the eight source-to-target pairs in the Conversion and source unit field, enter the value in the named source unit, and read the result in the target unit printed beside it. For example, square metres to square feet uses 10.76391, while square feet to square metres uses 0.09290304. The selected direction alone determines the factor.

How much error does the rounded factor add to a large order?

Almost none that anyone can measure. The stored meters to feet factor of 3.28084 differs from the exact reciprocal of 0.3048 by about one ten millionth, which works out at roughly one thousandth of an inch across a 1000 meter run. The error that actually damages a takeoff comes from the tape reading, the nominal product size and the pack rounding, not from the seventh decimal place of a constant.

Which everyday conversions does this tool not cover?

Cubic yards to cubic meters, board feet, linear feet of trim and temperature are all absent from the eight pairs. The table above lists the published metric equivalents for those units so the arithmetic can be done by hand, and the concrete, gravel and lumber tools on this site already work in the volume units their materials are sold in.

Should I convert before or after adding a waste allowance?

Either order returns the same number, because both operations are multiplications, but converting first keeps the audit trail readable. Convert the measured area, record it, apply the allowance, then divide by the selling unit. Anyone checking the sheet later can then see which figure came off the tape and which came from a judgment call about waste.

Related calculators

• Project Cost Calculator Convert every quantity into one unit system before a price per unit is applied, otherwise the cost total silently inherits the unit mismatch.
• Flooring Calculator Flooring boxes are labeled in square feet in the United States and in square meters elsewhere, so the m2-ft2 pair decides how many boxes reach the site.
• Grout Calculator Grout coverage charts are printed per square meter or per 100 square feet, and the area pair here puts your joint area on the same scale as the chart.
• Roofing Material Calculator Roof areas are quoted in squares of 100 square feet, which is 9.290304 square meters, so the plan area has to be converted before a bundle count means anything.
• Concrete Calculator Ready mix is sold by the cubic yard in the United States and by the cubic meter elsewhere, and the 0.764555 factor for that swap is listed in the table above.
• Lumber Calculator Board feet, nominal inch sizes and millimeter thicknesses all meet on one order, so the inch equivalents on this page keep the two labeling systems apart.

Sources

1. NIST Special Publication 1038: The International System of Units, Conversion Factors for General Use National Institute of Standards and Technology. Supplies every metric equivalent in the table on this page, including 0.3048 meters per foot, 0.09290304 square meters per square foot and 0.45359237 kilograms per pound, plus the rounding procedure and the 10 foot clearance example quoted in the rounding section. Accessed 2026-09-07.
2. Approximate Conversions from U.S. Customary Measures to Metric NIST Office of Weights and Measures. Publishes the two digit shortcut factors, such as 0.09 for square feet to square meters and 3.79 for gallons to liters, that this page contrasts with the longer factors the converter stores. Accessed 2026-09-07.
3. Approximate Conversions from Metric to U.S. Customary Measures NIST Office of Weights and Measures. Gives the reverse shortcut factors of 3.28 for meters to feet and 2.20 for kilograms to pounds, which match the leading digits of the stored factors quoted in the section on where the pairs come from. Accessed 2026-09-07.
4. Unit Conversion NIST Office of Weights and Measures. Sets out the NIST position that conversion factors belong in SP 811, SP 1038 and Handbook 44 Appendix C, which is why this page cites those publications rather than a general purpose reference table. Accessed 2026-09-07.

Prepared and maintained by Murat Yilmaz · Calculations checked against the cited sources and reference tests · Updated September 7, 2026

This is a planning result, not a supplier quote; sellers use different pack, bag, board, roll, and bundle conventions, so confirm the exact product label and selling unit before you order.