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Length & Distance Converter

Convert between all common metric and imperial length units with exact, internationally agreed conversion factors — every unit shown at once.

Millimeters (mm)1
Centimeters (cm)0.1
Meters (m)0.001
Kilometers (km)0.000001
Inches (in)0.03937
Feet (ft)0.003281
Yards (yd)0.001094
Miles (mi)0.000001
Nautical miles (nmi)0.000001

Anchored conversions from Millimeters (mm) use exact internationally agreed factors. Everything is computed locally, instantly.

The Foot That Refuses to Die

Almost every length unit on Earth is defined through the metre now, but some definitions still surprise people: one inch is exactly 25.4 mm by international agreement (since 1959, not a measurement), one nautical mile is exactly 1,852 m because it was defined as one minute of latitude, and one US survey foot differs from the international foot by about 2 parts per million — enough to matter in older land surveys, which is why the US officially retired the survey foot at the end of 2022.

Precision Errors This Tool Cannot Fix for You

  • Rounding early: convert first, round last. Rounding metres to 2 decimals and then converting to feet compounds the error.
  • Mixing survey and international feet in the same project produces discrepancies that only show up over long distances.
  • Aeronautical altitudes worldwide are in feet even in metric countries — converting them is almost always the wrong move.

How the Conversion Works

  1. Enter a value and pick the source unit — mm, cm, m, km, in, ft, yd, mi, or nmi.
  2. The tool converts to every other unit simultaneously, so one entry shows the complete picture.
  3. Conversion uses exact definitions (1 in = 25.4 mm exactly, since 1959).
  4. Copy any single result or the whole table.
Formula & Technical Standard
Anchored on the meter: 1 in = 0.0254 m (exact), 1 ft = 0.3048 m, 1 mi = 1609.344 m, 1 nmi = 1852 m.

Conversion Example

Height conversion
Input: 180 cm
Output: 1.8 m · 70.87 in · 5 ft 10.9 in
Body height between metric and imperial is one of the most common everyday conversions.
Road distance
Input: 26.2 mi
Output: 42.16 km
Marathon distance: the exact mile-to-kilometer factor gives 42.16 km, matching official race labeling.

Common Questions

Are the conversion factors exact?

Yes. Since the 1959 international agreement, the inch is defined as exactly 25.4 mm, and all other factors derive from exact definitions.

Why include nautical miles?

Aviation and marine navigation still use nautical miles (exactly 1852 m), so they belong in any complete length converter.

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