Length Converter
Convert length between millimetres, centimetres, metres, kilometres, inches, feet, yards, and miles.
How to use this tool
- Enter length and from unit in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your inches and the full breakdown beneath it.
Formula
All units convert to metres first, then to the target unit:
metres = input × factorfrom
output = metres ÷ factorto
Key factors: mm = 0.001 m | cm = 0.01 m | km = 1000 m | inch = 0.0254 m | foot = 0.3048 m | yard = 0.9144 m | mile = 1609.344 m
How it works
The converter uses metres as the universal base unit. The input value is multiplied by the metre-equivalent of its unit, and then divided by the metre-equivalent of each target unit. This two-step approach means only one set of constants needs to be maintained, and any unit pair can be converted without a dedicated formula.
A common mistake is confusing the imperial chain: there are 12 inches in a foot, 3 feet in a yard, and 1760 yards in a mile — people frequently misremember these as round numbers and introduce errors when converting manually between imperial units.
Worked example
Convert 1 metre to all length units
- Input: 1 metre (from_unit = meter), so the base value in metres = 1 × 1 = 1 m.
- Millimetres: 1 / 0.001 = 1000 mm. Centimetres: 1 / 0.01 = 100 cm. Kilometres: 1 / 1000 = 0.001 km.
- Inches: 1 / 0.0254 ≈ 39.3701 in. Feet: 1 / 0.3048 ≈ 3.2808 ft.
- Yards: 1 / 0.9144 ≈ 1.0936 yd. Miles: 1 / 1609.344 ≈ 0.0006214 mi.
1000 mm | 100 cm | 1 m | 0.001 km | 39.3701 in | 3.2808 ft | 1.0936 yd | 0.0006214 mi
Common mistakes to avoid
- Mixing up US survey feet and international feet — they differ by about 2 parts per million, which matters in land surveying but is invisible in everyday use.
- Entering a value in kilometres but leaving the source unit set to metres, producing a result 1,000 times too large.
- Confusing nautical miles with statute miles — a nautical mile is 1,852 m (about 6,076 ft), not the 5,280 ft of a land mile.
Key terms
- Metre (m)
- The SI base unit of length, defined as the distance light travels in 1/299,792,458 of a second in a vacuum.
- Inch (in)
- An imperial unit of length equal to exactly 0.0254 metres, or 1/12 of a foot.
- Yard (yd)
- An imperial unit equal to 3 feet (0.9144 m), commonly used in US sports and fabric measurement.
- Mile (mi)
- An imperial unit equal to 1760 yards or 1609.344 metres, used for road distances in the US and UK.
Frequently asked questions
- How many centimetres are in an inch?
- Exactly 2.54 cm. This is a defined, exact conversion, not an approximation.
- What is the difference between a metre and a yard?
- A yard is 0.9144 m, so it is about 8.56% shorter than a metre. For practical purposes, a metre is roughly 3.3 feet while a yard is exactly 3 feet.
- Why does the converter go through metres internally?
- Converting every unit to a single base (metres) and then to the target avoids maintaining a conversion table for every possible unit pair. With n units you need only n factors instead of n*(n-1) pair factors.