Length Converter
Convert between metres, feet, inches, miles, kilometres and every other common unit of length.
How to use this calculator
- 1Enter the value you want to convert.
- 2Pick the unit you are converting from and the one you want.
- 3The table below shows the same value in every other supported unit.
How the calculation works
result = (value × factor(from) ) / factor(to)- factor
- How many metres one unit represents
Every value is converted to metres first, then out to the target unit. This means n units need n factors rather than n² conversion pairs.
The inch, foot, yard and mile have been defined in terms of the metre since 1959, so these are exact conversions rather than approximations.
The nautical mile is defined as exactly 1,852 metres — roughly one minute of latitude.
Worked example
100 metres to feet
- 1.One metre is 1 metres, so 100 m is 100 metres.
- 2.One feet is 0.3048 metres, so divide: 100 ÷ 0.3048 = 328.08399.
- 3.Put another way, 1 m = 3.2808399 ft.
Result: 328.08399 ft
What "length" is measuring
Length describes how far apart two points are, measured in a straight line. It is the simplest physical quantity there is, which is also why it ends up borrowed into almost every other measurement — area is length squared, volume is length cubed, and speed is length divided by time.
The SI base unit is the metre. Every other unit of length in everyday use, metric or not, is now defined as an exact multiple of it, so converting between "old" units like the inch and "new" ones like the centimetre is not an approximation. It is fixed arithmetic, agreed by international treaty rather than measured from a physical object.
Two systems that never fully merged
Most of the world settled on one coherent system for length in the 19th and 20th centuries. A few countries, most visibly the United States, kept an older one running in parallel for everyday use.
- Metric (SI) — built entirely around the metre, scaled by powers of ten — millimetres, centimetres, metres, kilometres. Used for essentially everything, everywhere, outside a handful of countries.
- Imperial / US customary — inches, feet, yards and miles, descended from English units that predate any centralised standard. Still the everyday system in the United States, and still used for some purposes (road signs, house sizes) in the UK.
- Nautical and aviation units — the nautical mile, used at sea and in the air because it lines up with a minute of latitude, which makes chart navigation simpler than either metric or statute-mile arithmetic would.
- Astronomical units — light years and astronomical units, used once distances become too large for a kilometre figure to stay meaningful.
Why the United States still measures in feet and miles
The US Congress legalised the metric system for trade in 1866 and the country signed the Metre Convention in 1875, so the choice to keep using feet and miles day to day was never really about access to the alternative. It came down to the cost of switching: by the time metrication became a serious policy push in the 1970s, an enormous amount of infrastructure, tooling, road signage and industry standards were already built around inches and feet, and a voluntary conversion effort largely stalled.
The result is a split system. US science, medicine, the military and most manufacturing for export work in metric units, while construction, real estate, road distances and everyday conversation stay in feet, inches and miles — which is exactly the gap a converter like this one exists to bridge.
From footsteps to the speed of light
Early units of length were literally body parts — a foot, a cubit (forearm to fingertip), a span (hand width) — which made them convenient but inconsistent, since no two people’s feet are the same size. The metre was invented specifically to fix that: in the 1790s the French Academy of Sciences defined it as one ten-millionth of the distance from the North Pole to the Equator along the meridian through Paris, tying the unit to the planet rather than to any ruler or monarch.
That earthly definition proved hard to reproduce precisely, so the metre was later redefined against a physical platinum-iridium bar, then against the wavelength of light emitted by krypton-86. Since 1983 it has been defined as the distance light travels in a vacuum in exactly 1⁄299,792,458 of a second — tied to a constant of nature rather than to any object that could be damaged, lost or found to have changed size.
Common conversion pitfalls
A few mix-ups come up often enough to be worth flagging directly.
- Nautical vs statute miles — a nautical mile (1,852 m) is about 15% longer than the mile used on land (1,609.344 m). Mixing them up matters most for boating, flying and anything involving speed in knots.
- Feet and inch symbols — the prime (′) and double prime (″) marks used for feet and inches on drawings and real-estate listings are not the same characters as an apostrophe or quotation mark, though they are frequently typed as one.
- A light year is a distance, not a time — despite the name, it measures how far light travels in a year, not a duration — a common source of confusion in casual conversation.
- Compounding rounding — converting a value back and forth repeatedly through a rounded intermediate figure can drift slightly from the original number; this converter avoids that by always going through the exact base-unit factor.
What this assumes, and where it stops
Assumptions
- Conversion factors follow the internationally agreed definitions of each unit.
Limitations
- Results are computed in double-precision floating point, which is exact to about 15 significant figures.
- Very large or very small values are displayed in scientific notation to avoid misleading precision.
Common questions
How many feet are in a metre?
Exactly 1 ÷ 0.3048 = 3.280839895 feet. The common shorthand of 3.28 is accurate enough for most practical purposes, but the exact figure matters in engineering and surveying.
Why is a nautical mile different from a statute mile?
A nautical mile was originally one minute of arc of latitude, which makes navigation calculations straightforward on a globe. It is now defined as exactly 1,852 metres — about 15% longer than a statute mile.
Sources
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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