Length Converter

One converter for every length you are likely to meet: millimetres, centimetres, metres and kilometres on the metric side; inches, feet, yards and miles on the imperial side. Whether the job is a furniture dimension from a foreign catalogue, a running distance from an American app or a height quoted in the other system, enter the value, pick the units, and read the answer — no memorised factors, no crossed fingers.

Quick Answer

Every length conversion hangs on a few exact anchors: 1 inch = 2.54 cm exactly, 1 foot = 0.3048 m exactly, 1 mile = 1.609344 km exactly, and 1 m = 100 cm. Convert by chaining through these: for example, 180 cm = 5 ft 10.87 in.

Two Systems, One Set of Definitions

The world measures length two ways. The metric system scales by tens — 10 millimetres to a centimetre, 100 centimetres to a metre, 1,000 metres to a kilometre — and is used by science and by almost every country for daily life. The imperial and US customary system grew historically instead: 12 inches to a foot, 3 feet to a yard, 1,760 yards to a mile. It survives in everyday use in the United States and in pockets elsewhere — road distances and personal heights in Britain, aviation altitudes worldwide, screen sizes everywhere.

What makes a converter trustworthy is that the two systems are not independent. Since 1959, the international yard has been defined as exactly 0.9144 metres, which fixes the inch at exactly 25.4 millimetres and the foot at exactly 0.3048 metres. There is no measurement uncertainty in these factors at all: they are definitions, maintained by standards bodies such as NIST, so a conversion performed today matches one performed fifty years ago to the last digit. A converter's only real job is to apply the right defined factor and divide or multiply in the right direction — and to do it without dropping digits when the chain runs through several units, as a height in centimetres becoming feet-and-inches does.

The choice of input and output units is yours on every conversion. The converter does not assume a direction, which matters because some pairs are used almost exclusively one way — nobody converts miles into millimetres — while others, like metres and feet, flow constantly in both directions.

How to Use the Length Converter

1. Decide what you have and what you need: read the source unit off the drawing, listing or app, and the target unit from whoever or whatever will consume the answer.
2. Enter the numeric value into the input field, decimals included.
3. Select the unit you are converting from, then the unit you are converting to.
4. Read the result. For a rough check, metric-to-imperial length answers shrink or grow predictably: metres to feet roughly triples the number, kilometres to miles takes off about 40 percent.
5. If the answer is a height or a door width and comes out in decimal feet, translate the fractional part into inches by multiplying it by 12 (0.5 ft = 6 in) for the form people actually say aloud.
6. Convert each dimension of an object separately — length, width and height often come from different sources in different units — and label every converted figure with its unit.

A Person's Height, Carried Across Both Systems

Take a height of 180 cm, the sort of figure on a European ID card, and express it the American way. First, centimetres to metres: 180 ÷ 100 = 1.8 m. Then metres to feet using the exact factor: 1.8 ÷ 0.3048 = 5.9055 ft. Finally, the fractional foot into inches: 0.9055 × 12 = 10.87 in. So 180 cm = 5 ft 10.87 in, which most people would say as "five foot eleven" when rounding to the nearest inch.

Anchor values worth keeping:

• 1 mm ≈ 0.0394 in — about the thickness of a credit card's edge, 0.76 mm in reality
• 10 cm ≈ 3.94 in — a large smartphone's width territory
• 1 m ≈ 3.28084 ft — a metre is a long step
• 1 km ≈ 0.621371 mi — a 10 km run is 6.21 miles
• 1 yd = 0.9144 m exactly — slightly shorter than a metre
• 1 nautical mile = 1,852 m exactly — used at sea and in the air

Where Length Conversions Go Wrong

Area and volume are the first ambush: converting square metres to square feet uses the factor squared (about 10.7639), not the length factor 3.28084, and cubic conversions cube it. This tool converts lengths only — run a length through it and square the answer yourself only if the figure is a genuine side length. The second ambush is the survey foot: American land surveying long used a foot defined a few parts per million differently, a discrepancy small enough to ignore for furniture and large enough to matter across a county; the US survey foot was officially retired at the end of 2022, but old plats and maps still carry it.

Rounding chains are the third trap. Converting 5 ft to centimetres via a pre-rounded "1 ft = 30.48 cm" is exact, but converting via someone else's rounded "about 30 cm" throws away half a centimetre per foot, and the errors accumulate across a roomful of furniture. Convert once, from the original figure, with full precision, and round only the final presentation. Finally, check the label on imported goods: a "6-foot" cable sold internationally is usually exactly 1.83 m, but a "2 m" cable is 6 ft 6.7 in — not a six-footer — and the difference has disappointed many buyers. For frequent single-pair jobs, the dedicated pages are quicker: the CM to Inches converter and the Meters to Feet converter each open ready for their pair.

Every Unit, One Place

Most length headaches are not hard mathematics; they are the friction of two systems meeting in one document. Keep this converter open while reading foreign specifications, planning a room, comparing race distances or checking a delivery's dimensions, and the friction disappears. The whole family of unit tools, from weight to temperature, is collected on the converters category page.