Length Converter: cm, mm, Inches and Feet
Last updated: 2026-10-15
This length converter switches between metric and US customary units in both directions. Type a value into any box and the other three update as you type. Everything runs in your browser, so nothing you enter is uploaded and no internet connection is needed.
How the converter works
The widget above handles centimeters, millimeters, inches and feet. All four are tied together through centimeters: one inch is defined as exactly 2.54 cm, and one centimeter is exactly 10 mm. Because those links are exact, the arithmetic never adds error of its own. Only the number shown on screen is rounded.
The same idea covers the longer units. Meters, feet, yards and miles each have a fixed value in meters, so any pair of units can be converted by going through the meter as a middle step.
Units on this page
| Unit | Symbol | In inches | In meters |
|---|---|---|---|
| Inch | in | 1 | 0.0254 |
| Foot | ft | 12 | 0.3048 |
| Yard | yd | 36 | 0.9144 |
| Mile | mi | 63,360 | 1609.344 |
| Millimeter | mm | 0.03937 | 0.001 |
| Centimeter | cm | 0.3937 | 0.01 |
| Decimeter | dm | 3.937 | 0.1 |
| Meter | m | 39.37 | 1 |
| Kilometer | km | 39,370 | 1000 |
Every conversion runs through the meter: first turn the starting unit into meters, then turn meters into the target unit. That way there is only one number to trust per unit, instead of a separate formula for every possible pair.
Conversion formulas
| Conversion | Formula |
|---|---|
| Inches to centimeters | inches × 2.54 |
| Centimeters to inches | centimeters ÷ 2.54 |
| Millimeters to inches | millimeters ÷ 25.4 |
| Feet to meters | feet × 0.3048 |
| Meters to feet | meters × 3.2808 |
| Miles to kilometers | miles × 1.6093 |
| Kilometers to miles | kilometers × 0.6214 |
Quick conversions
| Value | Equals |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 30.48 cm |
| 1 yard | 0.9144 m |
| 1 mile | 1.6093 km |
| 1 meter | 3.2808 ft |
| 1 kilometer | 0.6214 mi |
| 10 cm | 3.937 in |
| 30 cm | 11.811 in |
| 100 cm | 39.370 in |
Are the conversion factors exact?
Yes. Since the 1959 international yard and pound agreement, the inch, foot, yard and mile have been defined by fixed metric values rather than by physical prototypes. These factors are exact definitions, not measurements.
| Unit | Exact definition |
|---|---|
| 1 inch | exactly 0.0254 m |
| 1 foot | exactly 0.3048 m |
| 1 yard | exactly 0.9144 m |
| 1 mile | exactly 1609.344 m |
How many digits appear is a display choice. Four significant figures is a sensible default; when a job needs more, apply the exact values above by hand. A result with more decimals is not more accurate, it is simply a longer version of the same exact number.
The US and the UK do disagree on some units, but not on length. A US gallon holds 3.785 liters and an imperial gallon holds 4.546 liters, roughly 20% more. An inch in New York is the same length as an inch in London, so there is no need to distinguish a "US inch" from an "imperial inch".
Exact by definition. Length is the one imperial family where the US and the UK agree. Volume units such as the gallon are a different story.
Where people use it
Shopping and hobbies. Listings often give screen size, drill bits or fabric in inches while the tape measure at hand reads centimeters. Convert once and buy with confidence.
Home projects. Furniture and appliance drawings usually run in millimeters, while a room is easier to picture in feet and inches. Converting tells you whether a sofa really fits through the doorway.
Sports and health. Race distances and heights are quoted in miles and feet in the US. Turning them into kilometers and centimeters makes international comparisons possible.
Schoolwork. Physics and math problems mix the two systems, and the converter is a fast way to check an answer.
When you need to measure something
A converter moves numbers, not objects. If you do not yet know how long something is, start with the on-screen ruler and use the converter afterwards.
The ruler needs one calibration first. Place a US dollar bill on the screen, it measures 156 × 66.3 mm, or a credit card, which is 3.37 in (85.60 mm) wide, and drag the green handle until the on-screen outline matches the object. After that the ruler shows true lengths, which you can read off in centimeters and feed into the boxes above.
A bank card makes a handy reference because ISO/IEC 7810 fixes its width at 85.60 mm in every country.
Everyday sizes in both systems
| Item | Inches | Millimeters |
|---|---|---|
| US Letter paper | 8.5 × 11 in | 215.9 × 279.4 mm |
| US dollar bill | 6.14 × 2.61 in | 156 × 66.3 mm |
| US quarter (diameter) | 0.955 in | 24.26 mm |
| Credit card | 3.37 × 2.13 in | 85.60 × 53.98 mm |
| Smartphone screen (diagonal) | 5.4–6.7 in | 137–170 mm |
Frequently asked questions
Which units does the converter handle?
The widget converts centimeters, millimeters and inches. The tables above also cover decimeters, meters, kilometers, feet, yards and miles.
Is 1 inch exactly 2.54 cm?
Yes, exactly, by definition since 1959. That is 25.4 millimeters.
How many feet are in a meter?
About 3.2808. Going the other way, one foot is 0.3048 meters.
Why does the result show only a few decimal places?
Four significant figures keeps the number readable. The underlying value is exact; only the displayed version is shortened.
Does the converter save what I type?
No. The calculation happens locally in your browser and the numbers are never sent anywhere.