How many centimetres are in an inch?

Exactly 2.54 cm. The inch is defined as 0.0254 metres, so one foot (12 inches) is 0.3048 m and one yard is 0.9144 m. These are exact definitions, not rounded approximations.

What is a nautical mile and how does it differ from a land mile?

A nautical mile is exactly 1852 metres, used in marine and air navigation because it corresponds to one minute of latitude. A statute (land) mile is 1609.344 metres, so a nautical mile is about 15 percent longer.

How does the converter stay accurate?

Every unit stores an exact factor in metres per unit. Your value is multiplied to metres and then divided into the target unit, so all conversions share one consistent base and avoid chained rounding.

What is an astronomical unit?

One astronomical unit (AU) is the average Earth-Sun distance, defined as 149,597,870,700 metres. It is convenient for stating distances within the solar system, where kilometres become unwieldy.

Can I convert very small or very large lengths?

Yes. The table spans nanometres up to astronomical units. Results that are extremely large or small are shown in scientific notation so the figures stay readable.

Length Unit Conversion Reference

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

Length is the most-converted physical quantity, and the units span an enormous range — from nanometres in chip design to astronomical units in space science. This reference lets you enter a value in any one unit and instantly read it in every other, using exact conversion factors rather than rounded constants.

How it works

Every unit is stored as an exact number of metres per unit, so the metre acts as a common base. Converting from one unit to another is two steps:

metres   = value × metresPerUnit[from]
result   = metres ÷ metresPerUnit[to]

Because all units route through the same metre base, there is no error from chaining conversions. The imperial units use their exact legal definitions — 1 inch = 0.0254 m, 1 foot = 0.3048 m, 1 mile = 1609.344 m — and the nautical mile is exactly 1852 m. The astronomical unit is the IAU-defined 149,597,870,700 m.

Tips and example

To convert 5 miles to kilometres: 5 × 1609.344 = 8046.72 m = 8.04672 km.
The inch-to-centimetre factor is exact and worth memorizing: 1 in = 2.54 cm, so 1 ft = 30.48 cm.
Use nautical miles, not statute miles, for marine and aviation distances — one nautical mile equals one minute of latitude.

Values far above or below the metre scale appear in scientific notation (for example a nanometre as 1e-9 m) so the numbers remain easy to read.