Enter a value and pick two units to convert instantly between metric and imperial lengths, with the exact conversion factor shown.
How to use this calculator
Enter the value you want to convert.
Pick the source unit (From) and the target unit (To) — the result updates instantly.
Read the exact conversion factor in the explanation so you can reuse it mentally.
Swap From and To to convert in the opposite direction.
Formula & method
Conversion through the SI base unit
result = value × factor(from → m) ÷ factor(to → m)
Every unit is defined in meters: 1 in = 0.0254 m · 1 ft = 0.3048 m · 1 yd = 0.9144 m · 1 mi = 1,609.344 m. Converting through meters keeps every pair of units exact.
Example
100 cm to inches: 100 × 0.01 m = 1 m, and 1 ÷ 0.0254 = 39.3701 inches.
Key insights
The inch has been defined as exactly 25.4 mm since 1959, so metric–imperial length conversions are exact, not approximate.
Handy anchors: 1 m ≈ 3.28 ft, 1 km ≈ 0.62 mi, 30 cm ≈ 1 ft, 5 km ≈ 3.1 mi.
Quick km-to-miles estimate: multiply by 0.6 — or use the Fibonacci trick, where 8 km ≈ 5 miles.
A statute mile (1,609.344 m) is shorter than a nautical mile (1,852 m), which is based on one minute of latitude.
How to interpret your result
Rounding
Results display up to 6 decimals, but the underlying conversion is exact — round to the precision your task actually needs.
Sanity checks
Use everyday anchors to spot input mistakes: a door is about 2 m (6.6 ft), a football field about 91 m (100 yd).
No cumulative error
Every conversion passes through meters, the SI base unit, so chained conversions introduce no compounding error.
Frequently asked questions
Are these conversions exact?
Yes — the international yard and pound agreement (1959) defines the inch as exactly 25.4 mm, so all imperial-metric length conversions here are exact, only display-rounded to 6 decimals.
What is the difference between a mile and a nautical mile?
A statute mile is 1,609.344 m; a nautical mile is 1,852 m, based on one minute of latitude. This tool converts statute miles.
Will you add other conversions?
Yes — weight, temperature, area and volume converters are planned next on the roadmap.
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