Length Converter
Converts length between metric and imperial — millimetres, centimetres, metres, kilometres, inches, feet, yards and miles — bidirectionally as you type. One inch is exactly 25.4 mm; every other factor follows from it.
How to use
- Enter a value in any unit's field.
- Every other unit updates instantly.
- Copy the value you need.
- For area or volume, use the dedicated converters — length factors do not square or cube themselves.
When you actually need this
- Translating a US product listing — a 55-inch screen, a 6-foot cable — into centimetres.
- Reading running or cycling distances between kilometres and miles.
- Converting furniture and floor-plan measurements when shopping across regions.
- Checking airline baggage size limits quoted in the other system.
Exact definitions, practical rounding
Since 1959 the inch is defined as exactly 25.4 mm, making the foot 0.3048 m and the mile 1,609.344 m — the conversions here are exact, not approximations. The rough rules people carry — an inch is about 2.5 cm, a mile about 1.6 km, a metre about 3.3 feet — are fine for intuition but drift at scale: 100 miles is 160.9 km, not 160. Screen sizes are diagonal inches, so a 55-inch TV is 139.7 cm across the diagonal, not the width — worth remembering when checking whether it fits the shelf.
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FAQ
How precise are the conversion factors in Length Converter?
The factors are the internationally defined exact values — one inch is exactly 25.4 millimetres, one pound is exactly 0.45359237 kilograms, and so on. Results are computed at full floating-point precision and only rounded for display.
Can I convert between metric and imperial units in both directions?
Yes. Enter a value in any field and every other unit updates at once, so the conversion works in either direction without switching modes or pressing a button.
Why does the last decimal place sometimes look off?
Because many conversions are irrational in decimal form and browsers use binary floating point, the final digit can differ by a tiny amount. The displayed value is rounded sensibly for everyday use; for laboratory or engineering work, carry the unrounded figure through your own calculation.