Length & Distance Converter

What Is a Length Converter?

A length converter translates a measurement of distance from one unit to another — metres to feet, kilometres to miles, inches to centimetres — without changing the physical distance itself. Length is the most fundamental of all measurements: every area, volume, speed, and density figure is ultimately built from it. Because the world runs on two parallel systems — metric (metre-based) and imperial/US customary (foot-based) — converting between them is an everyday need for engineers, builders, travellers, and students alike.

This converter works from the metre, the SI base unit of length, defined since 1983 as the distance light travels in a vacuum in 1/299,792,458 of a second. Every other unit is a fixed multiple of the metre — the inch is exactly 0.0254 m, the international foot exactly 0.3048 m, the mile exactly 1,609.344 m — so conversions are exact rather than approximate. Enter a value in any unit and read it instantly in all the others.

This is one category of the full Unit Converter — pair it with our percentage calculator or scientific calculator for related everyday maths.

Core Length Conversion Factors

Every conversion is a multiplication by one of these exact factors. Multiply to reach metres; divide to come back.

How to Use the Length Converter

1. 1

   Enter the value to convert

   Type the length you want to convert into the amount field — any positive number, from a fraction of a millimetre to a light-year.

2. 2

   Choose the 'from' unit

   Pick the unit your value is currently in — metres, feet, inches, miles, kilometres, yards, and more.

3. 3

   Choose the 'to' unit

   Pick the unit you want the answer in, or use the swap button to flip the direction instantly.

4. 4

   Read every unit at once

   Beyond the target value, the all-units table shows your length in every supported unit simultaneously so you never need a second conversion.

Best Practices for Length Conversion

• ✓Keep the inch exact at 25.4 mm. Since 1959 the inch is defined as exactly 25.4 mm, so all metric–imperial length conversions are exact. Don't use the old 'about 2.5 cm' approximation for engineering work.
• ✓Mind statute vs nautical miles. A nautical mile is ~15% longer than a statute mile. Using the wrong one in marine or aviation work introduces a real, compounding error over distance.
• ✓Round to your measurement's precision. If you measured to the nearest centimetre, report the converted value to a sensible precision — not the full 15 digits the math produces.
• ✓Use millimetres for engineering. Technical and machining drawings worldwide standardise on millimetres to avoid decimal-point and fraction errors that creep in with centimetres or inches.
• ✓Double-check unit symbols. 'm' is metres, 'mi' is miles, 'mm' is millimetres — a single dropped letter changes the answer by orders of magnitude. Confirm the symbol before trusting a figure.

Why Length Conversion Matters

Length sits at the base of nearly every other measurement, so an error in a length conversion propagates everywhere — into area (squared), volume (cubed), speed, fuel, and cost. The famous loss of NASA's Mars Climate Orbiter in 1999 came down to one team using imperial units and another metric: a units mismatch in distance-and-force data sent a $327 million spacecraft into the atmosphere instead of orbit.

On a smaller scale, the same risk shows up every day: a benchtop cut at the wrong unit, a curtain ordered to the wrong size, a part machined 1.6% off because someone used 2.5 instead of 2.54. A converter that uses exact, standards-based ratios removes the arithmetic as a source of error, leaving only the measurement itself to get right.