Length Converter
Convert between millimeters, centimeters, meters, kilometers, inches, feet, yards and miles.
Formula
Every unit converts through meters: multiply the value by its meters-per-unit factor, then divide by the target unit's factor. All factors are exact definitions (e.g. 1 inch = 0.0254 m).
Worked example
Convert 5 feet to meters: 5 × 0.3048 = 1.524 m. Convert 10 km to miles: 10 × 1000 ÷ 1609.344 = 6.2137 mi.
How to use the length converter
- Enter your number. Type the length you want to convert, such as 175.
- Pick your units. Choose the "from" unit and the "to" unit: millimeters, centimeters, meters, kilometers, inches, feet, yards or miles.
- Read the result. You get the converted value plus a line showing the factor used, for example 1 cm = 0.393701 in.
Worked example: 175 cm to inches
One inch is exactly 2.54 cm, so going from centimeters to inches means dividing by 2.54.
175 ÷ 2.54 = 68.8976, which rounds to 68.9 in. In feet and inches, that is 5 ft 8.9 in (68.9 − 60 = 8.9 in left over after 5 ft).
Why conversions are exact, not approximate
Until 1959, the inch was not quite the same everywhere. The US and the UK each defined their inch, foot and yard slightly differently. The gap was tiny, about two parts per million, but it mattered in engineering.
That year the US, UK, Canada, Australia, New Zealand and South Africa signed the international yard and pound agreement. It fixed the yard at exactly 0.9144 meters, which makes the inch exactly 2.54 centimeters. Since then, imperial units have been defined directly in terms of the metric system.
So when this converter turns inches into centimeters, nothing is estimated. Only the number shown on screen is rounded. The four exact factors are:
| Unit | Exact metric value |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 30.48 cm |
| 1 yard | 0.9144 m |
| 1 mile | 1609.344 m |
For a primary source, see the NIST Guide for the Use of the International System of Units (SP 811).
Which unit should you use?
- Millimeters (mm): small parts, screws, drill bits, phone and camera specs.
- Centimeters (cm): everyday sizes like height, clothing, furniture and parcels.
- Meters (m): rooms, fabric, fences and anything you can walk across.
- Kilometers (km): road distances, running routes and travel outside the US and UK.
- Inches (in): screen sizes, pipe and lumber dimensions, and US product specs.
- Feet (ft): height, room dimensions and ceiling heights in US building plans.
- Yards (yd): fabric, lawns, sports fields and some landscaping materials.
- Miles (mi): road distances and speed limits in the US and UK.
Planning a project? You may need to add extra material for waste. A percentage calculator can work out that 10% allowance once you have your length.
Everyday conversions, worked out
6 feet to centimeters
Factor: 1 ft = 30.48 cm. Multiply: 6 × 30.48 = 182.88 cm.
5 kilometers to miles
Factor: 1 mi = 1609.344 m, and 5 km is 5,000 m. Divide: 5,000 ÷ 1609.344 = 3.1069, so 5 km is 3.1069 mi. The same result comes from 1 km = 0.621371 mi, since 5 × 0.621371 ≈ 3.1069.
12 inches to centimeters
Factor: 1 in = 2.54 cm. Multiply: 12 × 2.54 = 30.48 cm. That is exactly one foot, which matches the factor in the table above.
Frequently asked questions
How many centimeters are in an inch?
There are exactly 2.54 centimeters in one inch. To convert inches to centimeters, multiply by 2.54.
How do I convert feet to centimeters?
Multiply the number of feet by 30.48. For example, 6 ft × 30.48 = 182.88 cm. For feet and inches together, convert the inches to feet first (divide by 12), or convert everything to inches and multiply by 2.54.
Is an inch exactly 2.54 cm?
Yes. The 1959 international yard and pound agreement defined the yard as exactly 0.9144 meters, which makes the inch exactly 2.54 cm. It is a definition, not a measured approximation.
Why do the US and UK use different units?
Both inherited inches, feet and miles from older English measures. The UK moved much of everyday life to metric from the 1960s and 1970s but kept miles on its roads. The US kept customary units in daily life and construction, while science, medicine and much of industry there use metric. Both countries define their units using the same exact metric values.
How precise are the results?
The calculations use the exact factors, so the only rounding is in what the page displays. If you need more digits for technical work, use the factor line shown with your result and calculate from it directly.
