Length Converter

Convert any length or distance between metric and imperial units — the inches-to-millimeters conversion machinists need, feet to meters, miles to kilometers and everything between — using the exact international definitions.

Results

Formula

All conversions route through the meter using exact definitions:
1 inch = 25.4 mm exactly · 1 foot = 0.3048 m · 1 mile = 1,609.344 m
The inch has been defined as exactly 25.4 mm internationally since 1959.

How to use this calculator

  1. Enter the value.
  2. Choose the unit you have and the unit you want.
  3. Press Calculate — the result and the unit relationship are shown.
Length Converter — how the calculation works, illustratedlength
Length Converter — how the calculation works, illustrated

Worked example

Convert 1 inch to millimeters.

  1. By international definition, 1 inch = 25.4 mm exactly.

Result: 1 inch = 25.4 millimeters.

Frequently asked questions

Why is the inch exactly 25.4 mm?

The 1959 international yard and pound agreement defined the yard as exactly 0.9144 meters, making the inch exactly 25.4 mm. There is no rounding in this conversion.

How many millimeters are in a foot?

304.8 mm — 12 inches × 25.4. Machinists use this constantly when mixing imperial drawings with metric tooling.

Miles to kilometers — quick mental shortcut?

Multiply by 1.6 for a close estimate (the exact factor is 1.609344). The Fibonacci sequence gives a famous party trick: 5 mi ≈ 8 km, 8 mi ≈ 13 km.

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