Length Converter
Metric and imperial length, converted both ways with a full reference table.
Length is where the metric and imperial systems collide most often — a screen measured in inches, a road in kilometres, a person in feet, a running track in metres. This converter handles nine units in both directions and shows the same value in all of them at once, so you can check a figure without converting it three times.
| Unit | Symbol | Value |
|---|
How it works
Pick the two units
Nine units covering metric, imperial and nautical measure.
Type a value
The result updates as you type, with the conversion factor spelled out.
Read the full table
The same measurement is shown in every supported unit underneath.
The inch has been exactly 2.54 cm only since 1959
Before that, it depended where you were. The British imperial inch and the American inch were defined from different physical standards and differed by roughly two parts per million — invisible for carpentry, significant for surveying and machine tooling. The 1959 international yard and pound agreement fixed the yard at exactly 0.9144 metres, which makes the inch exactly 25.4 millimetres by definition rather than by measurement.
One exception survived. American land surveys had been recorded for over a century in the older units, and re-measuring them was impractical, so the US survey foot was retained for that purpose — longer than the international foot by two parts per million, enough to shift a boundary by about a foot across a hundred miles. It was officially retired at the end of 2022, though older survey data still carries it.
This converter uses the international definitions throughout, which is what every modern standard, product specification and engineering drawing assumes. The values are exact rather than rounded: a mile is 1609.344 metres precisely, because it is defined as 5280 international feet.
Where the conversions go wrong in practice
The nautical mile is the unit most often mistaken for an ordinary mile, and the difference is not small — 1852 metres against 1609.344, about 15% further. It was defined as one minute of latitude along a meridian, which is why it survived: at sea and in the air, a distance that maps directly onto a chart is worth more than one that rounds nicely. A knot is one nautical mile per hour, for the same reason.
Rounding is the other recurring source of drift. Converting 6 feet to 1.83 metres and back gives 6.004 feet, which does not matter for a person’s height and does matter across a hundred repetitions in a bill of materials. Convert once from the original figure rather than converting a converted number, and keep the unrounded value in the calculation until the final display.
Screen and print sizes have their own convention worth knowing. A television or monitor measured in inches is measured diagonally, so a 27-inch screen is about 60 cm wide, not 69. And a paper size given in millimetres — A4 at 210 by 297 — has no exact inch equivalent, which is why A4 and US Letter never quite line up in a printer tray.