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Length Converter
Convert between metres, feet, inches, miles and kilometres.
In 1999 NASA lost a $327 million spacecraft because one engineering team calculated thruster force in pound-seconds and another team’s software expected newton-seconds. The Mars Climate Orbiter burned up in the Martian atmosphere, and the entire failure traced back to a units mismatch nobody caught before launch.
The metre was supposed to end exactly this problem
French scientists defined the metre in 1793 as one ten-millionth of the distance from the North Pole to the equator, measured along the line of longitude through Paris. The idea was a universal, nature-derived standard that no king, merchant or region could dispute or redefine to their own advantage — a genuine attempt to make length measurement politically and scientifically neutral.
It mostly worked. Nearly every country on Earth uses the metric system today. The holdouts — the United States most prominently — keep imperial units alive in everyday life and in enough engineering contexts that mismatches like the Mars orbiter still happen, more than two centuries after the metre was supposed to settle the question.
Length unit conversions
| Unit | In metres | Common use |
|---|---|---|
| 1 inch | 0.0254 m | Screens, tools, US/UK |
| 1 foot | 0.3048 m | Height, construction, US/UK |
| 1 yard | 0.9144 m | Fabric, sports fields, US/UK |
| 1 mile | 1,609.34 m | Road distances, US/UK |
| 1 kilometre | 1,000 m | Road distances, most of the world |
| 1 nautical mile | 1,852 m | Marine and air navigation, worldwide |
Where the imperial system quietly persists
- US road signs, construction blueprints and most home appliances still use feet and inches.
- Aviation altitude is measured in feet worldwide, even in fully metric countries, for historical air-traffic-control reasons.
- Nautical mile-based navigation is used at sea and in the air globally, independent of a country’s land-measurement system.
- UK road distances remain in miles, though most other UK measurements switched to metric decades ago — a genuinely split system.
Length conversion questions
How do I convert feet to metres?
Multiply by 0.3048. A 6-foot person is 6 × 0.3048 = 1.8288 metres tall. That 0.3048 figure was fixed as an exact international standard in 1959, ending centuries of slightly different national definitions of the foot.
Why did the Mars Climate Orbiter fail because of a units mistake?
One contractor’s navigation software calculated thruster performance in pound-force seconds, an imperial unit, while NASA’s ground software expected the metric equivalent, newton-seconds. Nobody cross-checked the units before the figures were used to correct the spacecraft’s trajectory, and the resulting error sent the orbiter too close to Mars, destroying it.
What is the exact definition of a metre today?
The distance light travels in a vacuum in 1/299,792,458 of a second. This 1983 definition ties the metre to the speed of light, a genuine physical constant, rather than to a physical bar of metal, which was the standard used for most of the twentieth century.
Why does the US still use feet and miles?
Metrication efforts in the 1970s met strong public and industry resistance, and without a legal mandate, the switch was never completed. Imperial units remain deeply embedded in construction, road signage and everyday habit, making a full changeover costly and politically unpopular ever since.
Is a nautical mile the same as a regular mile?
No. A nautical mile is 1,852 metres, based on one minute of latitude, while a standard mile is 1,609.34 metres, based on an old Roman and English land unit. They come from entirely different origins and differ by about 15%.
