Length Converter

One converter for ten length units

Single-pair pages answer one question at a time: meters to feet, or centimeters to inches. This page carries the full set in one place: millimeter, centimeter, meter, kilometer, inch, foot, yard, mile, nautical mile and the retired US survey foot. You type one value, pick the unit you have and the unit you want, and the result appears together with the same length restated in every other unit, so you can copy the row you need instead of running the tool again for each unit.

The default example is a 10 meter distance. The same 10 meters reads as 32.8084 feet, 393.701 inches, 10.9361 yards, 0.01 kilometer, 0.00621371 mile and 0.00539957 nautical mile.

Read the table as a sanity check. A yard holds 3 feet and a foot holds 12 inches, so the inch figure is 36 times the yard figure. The survey foot row differs from the international foot row only in the fourth decimal.

Every factor and where it came from

On July 1, 1959 the national standards labs of the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa signed one agreement: the yard would be 0.9144 meter exactly. That single sentence fixes the whole imperial side of this converter, because the inch is one thirty-sixth of a yard, the foot is one third of it, and the mile is 5,280 feet. Before 1959 the United States and British inches disagreed in the sixth decimal place.

The meter is the pivot every factor below is measured against. The SI Brochure published by the BIPM defines it through the speed of light, and the appendix tables of NIST Special Publication 811 list the same factors. Every one of them except the survey foot is an exact defined value rather than a rounded measurement.

Two anchors that make any conversion checkable

You do not need ten factors in your head, you need two. One meter is 3.28084 feet, so a 2 meter doorway is about 6.56 feet and a 30 meter bus is about 98 feet. One kilometer is 0.621371 miles, so a 5 km race is a 3.1 miler.

Worked with the exact factors: a 5 km fun run is 5,000 / 1,609.344 = 3.106856 miles. A marathon is labeled 42.195 km, and 42,195 / 1,609.344 = 26.218757 miles, the 26.2 on the race shirt. A person listed at 5 ft 9 in is 69 inches tall, and 69 x 0.0254 = 1.7526 meters, the 1.75 on a European form.

When a result looks wrong, reproduce it from an anchor before you doubt the tool. If a converter says 10 meters is 328 feet, the decimal is off by one place, because 3.28084 x 10 is 32.8.

Why the nautical mile owes nothing to the foot

The statute mile has an English legal history; the nautical mile came from the sky and the sea. One nautical mile is one minute of arc of latitude, one sixtieth of a degree, which makes charts readable: one degree of latitude is 60 nautical miles, and any distance you measure off a chart with dividers is already in nautical miles.

Earth is not a perfect sphere, so a minute of latitude varies from about 1,843 meters at the equator to about 1,862 meters at the poles. The International Hydrographic Conference of 1929 split the difference and fixed the nautical mile at 1,852 meters exactly. The United States kept its older value of 6,080.2 feet, about 1,853.24 meters, until 1954.

Converted, 1,852 / 1,609.344 = 1.15078 statute miles, and 1,852 / 0.3048 = 6,076.12 feet. That is why a knot is not a mile an hour: one knot is one nautical mile per hour, or 1.15078 mph. Aviation runs on the same mix in most of the world, with distances and speeds in nautical miles and knots but altitudes in feet.

The survey foot, 1893 to 2023

In 1893 the Mendenhall Order defined the American yard and pound in terms of the meter and kilogram, and the foot that came out of it was 0.3048006096 meter, written as the fraction 1,200/3,937. When the 1959 international agreement shortened the foot to 0.3048 meter, redefining every geodetic monument in the country at the same time was not practical, so the United States kept the old foot for surveying and named it the US survey foot. Two feet, each legal in its own lane: the international foot for trade, the survey foot for mapping.

The lane closed on January 1, 2023. NIST and the National Geodetic Survey announced the retirement of the survey foot, and from that date the international foot of 0.3048 meter is the only foot in United States use, except for interpreting legacy records. The two differ by about 2 parts per million: 5,280 survey feet make 1,609.34721869 meters, while the international mile is 1,609.344 meters, a gap of 3.2 millimeters per mile. Over a 100 mile state line that is 0.322 meter.

The survey foot stays in this converter for one job: checking measurements taken from old plats, deeds and state plane coordinate data recorded before 2023. For anything you measure today, the ordinary foot row is the answer.

Nominal versus actual sizes in lumber

Ask a lumberyard for a 2x4 and you will receive a board that measures about 1.5 by 3.5 inches. The name is the nominal size, the rough dimensions of the green board before it was dried and planed smooth. Surfacing removes material, so the actual size is smaller, and the difference is not slop, it is a standard: softwood boards are surfaced to published actual dimensions. Metric countries label the same board by its actual size in millimeters, 38 x 89 mm.

The two systems disagree on purpose. The inch dimensions are what an American tape measure shows, and the millimeter labels round them to whole millimeters, since 1.5 inches is 38.1 mm and 3.5 inches is 88.9 mm. Buying material is a nominal job: a wall framed from 2x4s is specified in nominal terms and framed on 16 inch centers. Fitting material is an actual job: a 2x4 does not slide into a 2 inch channel. Convert with the actual size whenever the question is whether two parts fit.

Two systems, one tape measure

Since 1959 the US customary and imperial length units are the same units, so a mile is a mile in Boston and in Birmingham; the systems still disagree on pints and gallons, but not on length. Where they appear is a patchwork. Road distances are in miles in the United States and the United Kingdom. Canada, Australia and the rest of the metric world sign their roads in kilometers. Aviation is nearly universal in nautical miles, knots and feet. Science, medicine and most engineering use SI units everywhere, the United States included.

Daily life absorbs the mix with hardware. American tape measures carry inch fractions on one edge and millimeters on the other. A sheet of plywood is sold as 4 by 8 feet in the United States, and the same sheet ships in metric markets as 1220 by 2440 mm, a rounding of 1,219.2 by 2,438.4 mm. A wrench set jumps between 10 mm and 3/8 inch because fastener standards grew up in both worlds. The practical skill is not conversion on paper, it is knowing which system the drawing, the recipe or the road sign in front of you speaks, then converting once.

The mistakes this converter catches

The first mistake is direction. Centimeters to inches means divide by 2.54: 30 / 2.54 = 11.811 inches. Multiply instead and 30 x 2.54 = 76.2, wrong by a factor of about 6.5. The anchor that catches it: an inch is bigger than a centimeter, so a length in inches must be a smaller number than the same length in centimeters.

The second is mixing feet-and-inches with decimal feet. A person who is 5 ft 9 in is 5.75 decimal feet, not 5.9, because 9 inches is 0.75 of a foot. Checked in meters: 5.75 x 0.3048 = 1.7526 meters, the same answer as 69 x 0.0254. Reading 5.9 as five feet nine inches puts almost two extra inches on a person.

The third is statute against nautical. A flight of 400 nautical miles is 400 x 1.15078 = 460.312 statute miles, and quoting 400 miles for it understates the trip by 60. Charts, aviation plans and boat logs are nautical; road signs and car odometers are statute.

The fourth is a slipped decimal on the big jumps. Kilometers to meters is times 1,000 and meters to millimeters is times 1,000 again, so a length quoted as 5,000 mm is 5 m, not 50 m. Convert once with exact factors, round the final answer once, and keep four or five significant digits until then.