Length converter
Pick two length units and type a number: the answer, the formula and the steps appear at once. Every factor comes from two exact definitions, 1 inch = 2.54 cm and 1 foot = 0.3048 m.
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The answer updates as you type.
1 centimeter =
0.393701in
Also written as about 3/8 in on a tape measure
Formula: in = cm ÷ 2.54
Show the steps
- Definition: 1 cm = 0.01 m (SI prefix centi); 1 in = 2.54 cm exactly
- 1 cm ÷ 2.54 = 0.393701 in
Definitions used: 1 cm = 0.01 m (SI prefix centi); 1 in = 2.54 cm exactly.
Source: NIST SP 811, Appendix B.8, checked on .
1 centimeter in every length unit
| Unit | Value |
|---|---|
| Millimeters (mm) | 10 |
| Meters (m) | 0.01 |
| Kilometers (km) | 0.00001 |
| Inches (in) | 0.393701 |
| Feet (ft) | 0.0328084 |
| Yards (yd) | 0.0109361 |
| Miles (mi) | 0.00000621371 |
| Nautical miles (nmi) | 0.00000539957 |
The table follows the amount and the “From” unit you set in the converter above.
How each length unit is defined
These are the definitions the converter uses, as written in the source next to each one. Nothing is rounded before the calculation.
| Unit | Definition | In meters |
|---|---|---|
| Millimeter (mm) | 1 mm = 0.001 m (SI prefix milli) | 0.001 |
| Centimeter (cm) | 1 cm = 0.01 m (SI prefix centi) | 0.01 |
| Meter (m) | SI base unit of length | 1 |
| Kilometer (km) | 1 km = 1000 m (SI prefix kilo) | 1,000 |
| Inch (in) | 1 in = 2.54 cm exactly | 0.0254 |
| Foot (ft) | 1 ft = 0.3048 m exactly (international foot) | 0.3048 |
| Yard (yd) | 1 yd = 0.9144 m exactly | 0.9144 |
| Mile (mi) | 1 mi = 1609.344 m exactly (5280 ft) | 1,609.344 |
| Nautical mile (nmi) | 1 nautical mile = 1852 m exactly | 1,852 |
Length conversion questions
What is the difference between metric and US length units?
Metric units (mm, cm, m, km) go up in powers of ten from the meter. US customary units are tied to it by definition: 1 inch is exactly 2.54 cm, 1 foot is 12 inches, 1 yard is 3 feet and 1 mile is 5,280 feet.
What is a nautical mile?
A nautical mile is exactly 1,852 meters, used at sea and in aviation. It is about 15% longer than the statute mile of 1,609.344 meters.
Are these factors exact?
Yes. Inch, foot, yard and mile are defined in terms of the meter, so converting between them involves no measured constant, only arithmetic. NIST SP 811 marks them as exact.
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Sources and limits
- NIST SP 811, Appendix B.8
NIST Special Publication 811, Guide for the Use of the SI, Appendix B.8: Factors for Units Listed Alphabetically (page updated August 18, 2025).
National Institute of Standards and Technology. Edition or effective date: . Text in force when checked on .
This is a calculation aid, not an official measurement service. Results are rounded to 6 significant digits for display. For trade, engineering, medical dosing or legal documents, confirm the figure in the official source. Nothing you type leaves your browser.