Length Converter
Convert between all common length and distance units in real time. Type a value in any unit and see instant conversion to millimeters, centimeters, meters, kilometers, inches, feet, yards, miles, and more. The multi-unit grid shows all values simultaneously with one-click copy for any measurement. Uses exact international yard definition (0.9144 m) for precise conversions.
What does this tool do?
The Length Converter provides real-time bidirectional conversion between 13+ length units. Enter a value in any field and all others update instantly. Supported units include metric (nanometer, micrometer, millimeter, centimeter, meter, kilometer) and imperial/US customary (inch, foot, yard, mile, nautical mile). Precision is maintained using IEEE-754 double precision with the international yard definition of exactly 0.9144 meters (1959). The tabular display lets you see your value in every unit at once and copy any individual value.
How it works
All conversions go through meters as the base unit. Each input value is converted to meters using the unit's definition, then from meters to all other units. Conversion factors use exact definitions: 1 inch = 0.0254 m (exact), 1 yard = 0.9144 m (exact by international agreement 1959). The nautical mile is defined as exactly 1852 meters. Precision is maintained throughout using JavaScript's Number (IEEE-754 double precision). Display precision is configurable (3, 6, or 9 significant figures). Values are rounded for display but full precision is maintained internally.
Features
- 13+ units: mm, cm, m, km, in, ft, yd, mi, nm, μm, nm, mil, light-year
- Edit any cell — every other unit recalculates instantly
- Tabular display with copy-on-click
- Switchable precision (3 / 6 / 9 significant figures)
- Recent conversions saved locally
- Exact conversion using international standards
- No rounding errors within display precision
How to use
- 1
Enter a value
Type in any unit field — metric or imperial. All other fields update immediately showing equivalent values.
- 2
Copy the unit you need
Click any value to copy it to clipboard. Use this for documentation, shopping, specifications, or communication.
- 3
Adjust precision
Choose significant figures based on your need: 3 for rough estimates, 6 for standard work, 9 for precision engineering.
- 4
Bookmark for daily use
Save the URL — the tool works offline once loaded and remembers recent conversions in local storage.
Common use cases
International commerce
Convert product dimensions between metric and imperial for international shipping, product listings, and specifications.
Construction and DIY
Convert between feet/inches and metric when working with mixed measurement systems on building projects.
Travel planning
Convert distances for trip planning — miles to kilometers for driving distances, understanding local signage abroad.
Science and engineering
Precise conversions between scientific units (nanometers, micrometers) and practical units for experiments and specifications.
Tips & best practices
- 1 inch is exactly 2.54 cm by definition — all inch-based conversions are exact, not approximations
- The international yard (0.9144 m) was defined in 1959 to resolve differences between US and UK yard standards
- A nautical mile is based on Earth's circumference (1 minute of arc) and is longer than a statute mile (1852m vs 1609m)
- A thou or mil is one thousandth of an inch (0.0254 mm), common in manufacturing and machining