Unit conversion
Length Converter
Converts length, where the imperial definitions are exact by agreement.
Result
Conversions use exact internationally defined factors where one exists, so results are precise to the digits shown.
Get a Free Business AuditHow the calculation works
Each unit is multiplied by its factor relative to a base unit. The imperial and US customary length units are defined exactly in terms of the metre by international agreement, with an inch exactly 25.4 millimetres, which means these conversions are exact rather than approximate.
What moves the number
- The factor for each unit pair.
- Precision required in the result.
- Whether the figure is a measurement or a nominal size.
- Surveying units, which have their own definitions.
Where this one goes wrong
Nominal sizes are not measurements, which means a two by four is not two inches by four inches and a half-inch pipe is not half an inch in any dimension you can measure, so converting a nominal designation produces a meaningless number. Convert measurements, not names. The US survey foot differed very slightly from the international foot and has been retired, which matters only in surveying and land records where the distinction accumulates over long distances.
Before you quote
- Convert measurements rather than nominal size designations.
- Round the result to the precision the input justifies.
- Note that surveying records may use historical definitions.
Questions
About this calculator
Are inch to millimetre conversions exact?
Yes. An inch is defined as exactly 25.4 millimetres by international agreement, which makes the imperial and metric length conversions exact rather than approximate. The precision of a result is limited by the input, not by the conversion.
Can I convert a nominal size?
Not meaningfully. A two by four is not two inches by four inches and a half-inch pipe is not half an inch anywhere you can measure, so converting the designation produces a number that describes nothing physical.
What is the survey foot?
A very slightly different historical definition used in US surveying and land records, now retired. The difference is negligible over short distances and accumulates over long ones, which is why it mattered for land measurement and nowhere else.
Common length conversions
| From | Equals |
|---|---|
| 1 Feet | 304.8 Millimetres |
| 1 Feet | 30.48 Centimetres |
| 1 Feet | 0.3048 Metres |
| 1 Feet | 0.000305 Kilometres |
| 1 Feet | 12 Inches |
| 1 Feet | 1 Feet |
| 1 Feet | 0.333333 Yards |
| 1 Feet | 0.000189 Miles |
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How to use this calculator
- Value. Enter your own figure; the page starts at 10.
- From. Enter your own figure; the page starts at Feet.
- To. Enter your own figure; the page starts at Metres.
The result updates as you type, so you can try a figure, see what it does to converted value, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Value | 10 |
| From | Feet |
| To | Metres |
What comes out
| Result | Value |
|---|---|
| Converted value main result | 3.048 |
| Conversion factor | 0.3048 |
10 Feet equals 3.048 Metres.
How sensitive the answer is
Holding everything else steady and changing only value, this is what happens to converted value. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Value | Converted value |
|---|---|
| 5 | 1.524 |
| 7.5 | 2.286 |
| 10 example above | 3.048 |
| 15 | 4.572 |
| 20 | 6.096 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Value
- A number, starting at 10.
- From
- Choose from Millimetres, Centimetres, Metres, Kilometres, Inches, Feet, Yards, Miles, Nautical miles.
- To
- Choose from Millimetres, Centimetres, Metres, Kilometres, Inches, Feet, Yards, Miles, Nautical miles.
What the results tell you
| Result | What it is |
|---|---|
| Converted value | The headline result. A number. |
| Conversion factor | A number. |
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