Length Converter
Convert between any common length units — metric (mm, cm, m, km) and imperial (inch, foot, yard, mile) — plus less-common ones like nautical mile, light-second, and astronomical unit.
Enter a length
Tap any value to copy it.
How to use this calculator
1. Type a value
Enter the number you want to convert in any unit.
2. Pick the source unit
The dropdown covers metric (nm → km), imperial (inch → mile + nautical mile), and astronomical scales (light-year, AU, parsec).
3. Or click a preset
Quick presets fill common values like a marathon (42.195 km), 100m sprint, or 6 feet for height.
4. Read the grid
Eight common units appear at once. Less common units (nautical mile, light-year) show in the share-able state.
About the units
Metric base
The meter is the SI base unit of length. Everything else metric is a power of ten: 1 km = 1,000 m, 1 cm = 0.01 m, 1 mm = 0.001 m, 1 μm = 10-6 m, 1 nm = 10-9 m.
Imperial conversions
1 inch = 25.4 mm (exact, by definition). From there: 1 ft = 12 in, 1 yd = 3 ft, 1 mi = 5,280 ft.
Nautical and astronomical
1 nautical mile = 1,852 m (used in aviation and sea navigation). 1 light-year ≈ 9.461 × 1015 m. 1 AU = average Earth-Sun distance ≈ 149.6 million km. 1 parsec ≈ 3.26 light-years.