Length Converter
Convert between metric, imperial, and nautical/astronomical length units — millimeters to miles, meters to feet, and beyond — with every unit updating live as you type.
Common Length Conversions
- 1 inch = 2.54 cm
- 1 foot = 0.3048 m
- 1 yard = 0.9144 m
- 1 mile = 1.60934 km
- 1 meter = 3.28084 ft
- 1 kilometer = 0.62137 mi
- 1 nautical mile = 1.852 km
Understanding Length Units
The metric system (millimeters, centimeters, meters, kilometers) scales by powers of 10, so converting between metric units is just a matter of moving the decimal point. The imperial/US customary system (inches, feet, yards, miles) uses less regular ratios — 12 inches to a foot, 3 feet to a yard, 1,760 yards to a mile — inherited from historical units of measurement. Most of the world uses the metric system for everyday measurement; the United States is the largest country that still primarily uses imperial units.
A nautical mile (1,852 meters) is based on the distance covered by one minute of latitude on Earth's surface, which makes it especially convenient for marine and air navigation, where positions are tracked in degrees and minutes. A light year, despite its name, measures distance rather than time — it's how far light travels in one Julian year (365.25 days) through a vacuum, roughly 9.46 trillion kilometers, and is used to express astronomical distances that would otherwise require inconveniently large numbers of kilometers or miles.
Frequently Asked Questions
About this calculator
This length converter lets you enter a value in any of 12 units and see it instantly converted to all the others — from nanometers up to light years. It covers the metric system, the imperial/US customary system, and specialty units used in navigation and astronomy, so you don't need to remember conversion factors or do the math by hand.
- 12 units at once — Nanometers, micrometers, millimeters, centimeters, meters, kilometers, inches, feet, yards, miles, nautical miles, and light years, all converted simultaneously.
- Live conversion — Type a value into any unit and every other field updates instantly — no need to click a button or pick a 'from' and 'to' unit.
- Handles extreme scales — Correctly formats very large or very small results (like converting millimeters to light years) using scientific notation when needed.
- Metric and imperial together — No need to switch tabs or modes — every metric and imperial unit is visible and editable at the same time.
- Quick reference table — Common conversions (inches to cm, miles to km, and more) are listed for fast lookup without typing anything.