About Length Conversion
Length is one of the seven base quantities in the International System of Units (SI), and it is the quantity most commonly converted between systems. The metric system is used in almost every country for everyday measurement, while the imperial system — feet, inches, miles — remains standard in the United States, the United Kingdom for road distances, and a handful of other contexts worldwide.
Because both systems are still in active daily use, quick conversion between them is one of the most useful tools you can keep on hand. The mathematics is simple: every unit has a fixed, exact relationship to the metre (the SI base unit), so any conversion is just two multiplications.
The 14 units supported
| Unit | Symbol | Metres |
|---|---|---|
| Nanometre | nm | 0.000000001 |
| Micrometre | µm | 0.000001 |
| Millimetre | mm | 0.001 |
| Centimetre | cm | 0.01 |
| Metre | m | 1 |
| Kilometre | km | 1000 |
| Inch | in | 0.0254 |
| Foot | ft | 0.3048 |
| Yard | yd | 0.9144 |
| Mile | mi | 1609.344 |
| Nautical mile | nmi | 1852 |
| Astronomical unit | AU | 149597870700 |
| Light year | ly | 9460730472580800 |
| Parsec | pc | 30856775814913673 |
Common conversions
| From | To | Factor |
|---|---|---|
| 1 inch | Centimetres | 2.54 exactly |
| 1 foot | Centimetres | 30.48 exactly |
| 1 yard | Metres | 0.9144 exactly |
| 1 mile | Kilometres | 1.609344 exactly |
| 1 nautical mile | Metres | 1852 exactly |
| 1 kilometre | Miles | 0.621371… approximately |
Common use cases
Travel & Distance
Convert miles to kilometres for road signs abroad.
Construction
Convert between feet/inches and metric for building plans.
Cooking & Sewing
Convert inches to centimetres for fabric and pattern sizes.
Science & Lab
Convert nanometres, micrometres and millimetres for measurements.
Screen Sizes
Convert diagonal inches to centimetres for monitors and TVs.
Astronomy
Convert between AU, light years and parsecs.
Privacy and accuracy
This length converter runs entirely in your browser. All conversions use exact definitional factors, so the results are as precise as the input. Nothing is uploaded, stored or logged — safe for confidential measurements and private engineering work.