Length & Distance Converter
Convert a length or distance between fourteen units, from the nanometre up to the parsec. Imperial and metric lengths have shared an exact definition since 1959, so these are not approximations — one inch is precisely 0.0254 metres, and every other factor follows from that.
How to use this tool
- Type the length you want to convert into the Value field. Decimals, negative numbers and scientific notation such as 1.5e3 are all accepted.
- Pick the unit your number is currently in from the From menu.
- Pick the unit you want the answer in from the To menu.
- Read the result as you type — there is no button to press.
- Switch on “Show every equivalent unit” to see the same distance expressed in all fourteen units at once.
The formula
Length uses the metre as its base unit. Imperial and US customary lengths have been defined in terms of the metre since the 1959 international yard and pound agreement, so these conversions are exact rather than approximate.
metres = value × metres_per_unit
result = metres ÷ metres_per_target- metres_per_unit
- Exact metre value of the input unit
- metres_per_target
- Exact metre value of the output unit
One inch is exactly 0.0254 metres by definition. Astronomical units are exact too: the astronomical unit is fixed at 149,597,870,700 m and the parsec follows from it as AU × 648000/π.
Worked examples
Metres to feet for a room measurement
- Given
- 4.5 metres
- Result
- 14.763780 feet
4.5 m ÷ 0.3048 m per foot = 14.76378 ft. Because a foot is defined as exactly 0.3048 metres, this division is exact rather than approximate.
A marathon in kilometres
- Given
- 26.2 miles
- Result
- 42.164806 kilometres
26.2 mi × 1609.344 m per mile = 42,164.8 m, then ÷ 1000 = 42.1648 km. The official marathon distance is 42.195 km, slightly longer than 26.2 miles.
How far is a light-year?
- Given
- 1 light-year
- Result
- 9,460,730,472,580,800 metres
Light travels 299,792,458 metres per second. Multiplied by the seconds in a Julian year (365.25 × 86,400), that gives roughly 9.46 quadrillion metres.
Frequently asked questions
The factors themselves are exact. Since the 1959 international yard and pound agreement, the inch has been defined as exactly 0.0254 metres, so feet, yards and miles all convert exactly. Only the displayed result is rounded, and the underlying calculation keeps full precision.
A statute mile is 1,609.344 metres and is used on land. A nautical mile is 1,852 metres — about 15% longer — and is used at sea and in aviation because it corresponds to one minute of latitude, which makes chart navigation straightforward.
They measure the same thing by different methods. A light-year is how far light travels in a year. A parsec is the distance at which one astronomical unit subtends one arcsecond, which works out to about 3.26 light-years. Astronomers tend to prefer parsecs because they fall directly out of parallax measurements.
Yes. A negative length is meaningless as a physical size, but it is perfectly sensible as a displacement or a difference — for example a drop in elevation. The converter handles the sign correctly rather than rejecting it.
The converter switches to significant figures when a result is very large or very small. Showing a fixed four decimal places would turn that answer into 0.0000, which hides the number entirely. Six significant figures keeps the information visible at any scale.
Yes. Micron is the older name for the micrometre, one millionth of a metre. The name was officially dropped in 1967 but is still widely used in engineering and filtration. This converter accepts either term.
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