What this calculator does
Every length unit here converts through a single base unit, the metre, so a figure in any unit can reach any other unit through one multiplication and one division, never a direct table of every possible pairing.
The result includes the full ladder of equivalents alongside the one conversion you asked for, because a single figure rarely answers the question on its own: knowing that 100 cm is also roughly 39.4 inches and 3.28 feet at the same time is usually more useful than just one of those.
The formula
Every unit has a fixed factor expressing it in metres: a mile is exactly 1,609.344 metres, an inch exactly 0.0254. Converting from one unit to another multiplies by the first factor to reach metres, then divides by the second to leave metres behind. Metric units are exact by definition; the imperial-to-metric factors are themselves exact too, fixed by international agreement since 1959.
| Term | Meaning |
|---|---|
| Base unit | The common unit every other unit converts through: the metre here. |
| Factor | How many base units make up one of a given unit. |
| Nautical mile | Exactly 1,852 metres, defined from one minute of latitude: used at sea and in aviation rather than on land. |
The inputs explained
| Field | What to enter |
|---|---|
| Value | The value to convert. |
| From | The unit you are converting from. |
| To | The unit you want the answer in. |
When to use it
Reading a tape measure in the other system
A builder working in feet and inches on a metric plan, or the reverse, needs this conversion constantly: 100 cm and 39.37 inches are the same length, just described two different ways.
Converting a race, run or flight distance
Road races are usually metric, US road signage is usually imperial, and sea and air distances use nautical miles: three different units for what might be the same trip.
Checking a size against an imperial spec
Screen sizes, pipe diameters and paper formats are often specified in inches even in metric countries, so converting a metric measurement to inches is a common check before buying.
Scaling a distance measured astronomically
The light year sits at the far end of this list, 9.4607 × 10¹⁵ metres, included for the rare occasion a length calculation needs to span from millimetres to interstellar distances.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How far is one of each unit, in kilometres?
A single unit of measurement from millimetres up to nautical miles, each converted to kilometres to compare their true scale.
| From | In kilometres |
|---|---|
| Millimetre | 0.000001 km |
| Centimetre | 0.00001 km |
| Metre | 0.001 km |
| Inch | 0.0000254 km |
| Foot | 0.0003048 km |
| Yard | 0.0009144 km |
| Mile | 1.609344 km |
| Nautical mile | 1.852 km |
Converting 100 centimetres to other units
A single value of 100 centimetres, one metre, expressed in each of the other units in turn.
| To | Result |
|---|---|
| Millimetres | 1,000 mm |
| Metres | 1 m |
| Inches | 39.37007874 in |
| Feet | 3.2808399 ft |
| Yards | 1.0936133 yd |
| Miles | 0.00062137 mi |
Questions
How many centimetres are in an inch?
Exactly 2.54 cm, fixed by international agreement in 1959. Every other inch-to-metric conversion in this calculator derives from that one exact figure.
What is the difference between a nautical mile and a regular mile?
A nautical mile is 1,852 metres, defined from the Earth’s circumference: one minute of latitude. A statute mile is 1,609.344 metres, an older land-measurement unit. They are close in size but not interchangeable in navigation.
Why isn’t 100 cm exactly equal to a round number of inches?
Because the metric and imperial systems were defined independently. The metre traces back to a fraction of the Earth’s meridian; the inch to older English units. Their ratio, 2.54, was fixed by treaty, not designed to produce round conversions.
How do I convert a very small or very large length, like a light year?
Select it as either the "from" or "to" unit and enter any value: the calculator handles the full range from millimetres to light years using the same base-unit method throughout.
Is a UK mile the same as a US mile?
Yes: the international statute mile, 1,609.344 metres, is the same length in both countries and is what this calculator uses. Only the nautical mile is a genuinely different, separate unit.
For area rather than a single dimension, see the area converter. For speed, which combines length and time, use the speed converter.