Length Converter (mm, cm, m, km, in, ft, yd, mi)
Type a length, pick the source unit, and see the conversion to every other common unit at once. Uses internationally agreed conversion factors.
How it works
How length conversion works
All length units can be expressed in meters using a fixed conversion factor. To convert from unit A to unit B, multiply the value by 'meters per A' and divide by 'meters per B'. The factors are not approximations — since 1959, the international yard has been defined as exactly 0.9144 meters, which fixes inches at exactly 0.0254 m and miles at exactly 1609.344 m.
This calculator stores the meter-equivalent for every unit and applies the formula directly, so the only error is from how many digits you enter. The result is shown to up to eight significant digits, which is enough for engineering, navigation, and most scientific work.
Common conversions you'll need
1 inch = 2.54 cm exactly. 1 foot = 30.48 cm. 1 yard = 91.44 cm. 1 mile = 1.609344 km. Going the other direction, 1 cm ≈ 0.3937 in and 1 km ≈ 0.6214 mi.
For everyday tasks like shipping, height conversion, and cooking, the all-units panel below the main input shows every conversion at once — no need to look up factors separately.
Why the imperial system isn't going away
Three countries — the United States, Liberia, and Myanmar — still use imperial units in everyday life, and the US aviation industry uses feet and nautical miles internationally. Anyone working across these systems will reach for a converter often.
British units of length were standardized by Parliament in 1824 (the Imperial system) and re-defined in metric terms in 1959 to remove drift between US and UK measurements. Modern imperial units are therefore exact rationals of the meter.
Frequently asked questions
›Are these conversions exact?
Yes. Since 1959 the international yard is defined as exactly 0.9144 m, which makes every imperial-to-metric conversion in this tool an exact rational number.
›What's the difference between US and UK miles?
Both are equal to 1609.344 m today. The US 'survey mile' (used in some land surveying) differs by about 3 mm per mile and is not used here.
›Why doesn't the result use scientific notation?
We use grouped decimal notation up to 8 significant digits because it's easier to read for most everyday work. For very small or very large values, you can still copy the number and reformat it.
›Can I convert between two imperial units?
Yes. The tool routes everything through meters internally, so any pair (e.g., feet to inches) works the same way.
›Is this calculator accurate enough for engineering?
Eight significant digits is sufficient for civil engineering, navigation, and most lab work. For metrology-grade work, refer to NIST's published factors.
›Does the calculator work offline?
Once the page is loaded, all conversions run entirely in your browser, so no network connection is needed for subsequent calculations.
›How do I convert centimeters to feet and inches?
Convert cm to inches first, then split into feet (12 inches each) and remaining inches. Many height calculators use this two-step approach.
›What's the smallest unit you support?
Millimeters. If you need micrometers or smaller, multiply the millimeter result by 1000.
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