Inch to Meter Converter

One inch is exactly 0.0254 meters

The conversion has no approximation in it. An inch is defined as 25.4 millimetres, so 1 in = 0.0254 m by definition rather than by measurement. A foot is twelve of them, 0.3048 m, a yard is 0.9144 m, and none of those numbers will ever gain another decimal place.

The definition dates from 1959, when English speaking countries agreed to reconcile their slightly different inches and pounds. The US side was published as Federal Register Notice 59-5442 and took effect on July 1, 1959. NIST SP 811, Appendix B lists the result as 2.540 000 E-02 meters per inch, with an asterisk marking the factor as exact. The older US survey foot, at 1200/3937 m, survived for geodetic work until it was retired at the end of 2022, which is why old survey plats can differ from a modern conversion by 2 parts per million.

So 6 feet is 6 x 0.3048 = 1.8288 m, 80 inches is 2.032 m, and 0.001 in is 0.0000254 m, or 25.4 micrometres. The arithmetic is one multiplication, so the errors happen in what you feed it.

This page converts to meters and handles inches as fractions, because that is what a US tape measure shows and what a metric drawing asks for. Inches to centimeters stops one unit short of a meter and suits fabric and paper, while feet to meters assumes whole feet and skips the inches entirely. Neither handles 5 ft 9 1/2 in, and that mixed reading is the common case on a job site.

Fractional inches in meters

A tape measure in the US is graduated in halves, quarters, eighths and sixteenths, and a metric drawing wants a decimal. The sixteenth is the finest mark on a standard tape, so it sets the resolution for most trade work: 1/16 in is 1.5875 mm, which is 0.0015875 m.

The fractions reduce in a pattern that makes mental arithmetic easier. Every halving of the fraction doubles the millimetre value, so 1/16 in is 1.5875 mm, 1/8 in is 3.175 mm, 1/4 in is 6.35 mm and 1/2 in is 12.7 mm. The meter values move by the same factor: 0.0015875, 0.003175, 0.00635, 0.0127.

The calculator adds the fraction to the whole inches instead of rounding it first, so 5 ft 9 1/2 in becomes 69.5 in and then 1.7653 m. Round the fraction to a decimal too early and a stack of 20 boards drifts by a few millimetres, which is enough to throw a cabinet run out of level.

Feet plus inches in one number

Mixed readings are where most conversion mistakes happen, because the two parts need different treatment. Multiply the feet by 12 to get inches, add the inches and the fraction, then multiply the total by 0.0254 once. Adding meters from the feet and meters from the inches separately and then adding those works too, but it doubles the chance of a slip.

Height is the case people bring to a converter, and it is the one where the answer is quoted in two units at once: 5 ft 9 1/2 in is 1.765 m on a European form and 176.5 cm on a passport application.

Doorways are the other common mixed case. A US interior door is 80 in tall, which is 2.032 m, and a European door frame is often 2.0 m, so a 2.032 m door does not fit a 2.0 m opening without trimming. That 32 mm gap is the reason the door row in the table above matters more than the height rows.

Meters back to inches

The reverse conversion divides by 0.0254, which is the same as multiplying by 39.3701. That number is worth remembering as a sanity check: a meter is a bit more than a yard, and a yard is 36 inches, so anything near 39 inches per meter is in the right range.

The fraction column is not exact and does not pretend to be. 1 m is 39.3701 in, while 3 ft 3 3/8 in is 39.375 in, a difference of 0.0049 in or 0.12 mm. That is the resolution of a sixteenth, and it is why a metric drawing converted to fractions for a US shop needs a tolerance note rather than a promise of exactness.

Common lengths, and what they are in meters

Some conversions come up often enough to be worth memorizing. The ones below cover paper, screens, lumber and openings, and all come from the same multiplication, so the only thing to check is which dimension of the product the number refers to.

The A4 row is a good check on the whole system. The ISO 216 standard defines A4 as 210 mm by 297 mm, which is 11.6929 in by 8.2677 in, and the meter value needs no conversion because 297 mm is 0.297 m by definition. A US Letter sheet is 8.5 in by 11 in, or 0.2159 m by 0.2794 m.

The lumber row trips people up for a different reason. A 2x4 is not 2 in by 4 in. The American Softwood Lumber Standard, NIST PS 20-25, sets the dressed size at 1-1/2 in by 3-1/2 in, so the width in metric is 0.0889 m and the thickness is 0.0381 m. Converting the nominal 4 in instead gives 0.1016 m, a 14 percent error that will show up in any cabinet or shelf layout.

The digits that matter when you round

Three decimals of a meter is one millimetre, which is the natural place to stop for anything built by hand. Ten inches is 0.254 m exactly, but 3.937 in is 0.1000 m only after rounding: 3.937 x 0.0254 = 0.0999998, and the difference is 0.2 micrometres. Rounding at the end is safe; rounding the factor is not.

The common shortcut is 39.37 inches per meter instead of 39.3701. On a 1 m length the error is 0.0001 in, invisible. On a 100 m length it is 0.0079 in, about 0.2 mm, which is still inside most construction tolerances and outside a machinist's. The same logic applies to 0.0254: cutting it to 0.025 gives an error of 1.6 percent, which is 16 mm on a meter and enough to ruin a frame.

The survey foot is the other trap. Before 2023, US geodetic work used 1200/3937 m per foot, which is longer than the international foot by 2 parts per million. Over 1,000 ft that is 0.002 ft, or 0.6 mm, and over a mile it is 0.01 ft. Small, but a coordinate system built on the wrong foot accumulates the error across a whole parcel.

One more: significant figures follow the input, not the calculator. A measurement of 80 in, read to the nearest eighth, supports 2.032 m but not 2.0320 m.

How to write a metric length in a US document

Mixing the two systems in one drawing is where documents go wrong. The convention that survives review is to give the primary unit first with its symbol, put the converted value in parentheses, and round the conversion to one more decimal than the original resolution. That gives 80 in (2.032 m) and 5 ft 9 1/2 in (1.765 m), not 80 in (2.03200 m).

Below a meter, millimeters are the working unit in most of the world: a 297 mm sheet, an 89 mm stud, a 25 mm screw. Meters take over above about a meter, and centimeters mostly survive in clothing and body measurements. Pick the unit that matches the drawing you are working from rather than converting twice, because each conversion is a chance to invert the factor.

There is no period after in, m, mm or ft, and there is a space between the number and the symbol: 2.032 m, not 2.032m. That convention makes 0.0254 m look correct on a drawing and 0.0254m look like a typo.

This page does exact unit arithmetic on the numbers you enter. It does not know your tolerance, your drawing standard or which dimension of a product you measured. Confirm the specification with the manufacturer or the standard before cutting anything.