Length Unit Conversion Reference
Length is the most commonly converted unit type worldwide. Whether you're reading a road sign in miles, following a recipe that lists centimeters, or interpreting property measurements in feet, our length converter handles all standard units instantly. All conversion factors are sourced from NIST Handbook 44 and the international yard and pound agreement of 1959, ensuring precision to at least 10 significant digits.
The 10 Units We Support
Our length converter covers the full spectrum of everyday and scientific use cases:
- Meter (m) — the SI base unit of length. Defined since 2019 as exactly 1/299,792,458 of the distance light travels in one second in a vacuum.
- Kilometer (km) — 1,000 meters. The standard unit for road distances in metric countries.
- Centimeter (cm) — 0.01 meters. Commonly used for body measurements, clothing sizes, and small dimensions.
- Millimeter (mm) — 0.001 meters. Used in engineering drawings, medical imaging, and precision manufacturing.
- Mile (mi) — exactly 1,609.344 meters by international agreement. The standard road distance unit in the United States, United Kingdom, and Myanmar.
- Yard (yd) — exactly 0.9144 meters. Used in American football field dimensions, fabric measurements, and some construction trades.
- Foot (ft) — exactly 0.3048 meters. Widely used in the US and UK for height measurements, altitude (aviation), and residential property dimensions.
- Inch (in) — exactly 0.0254 meters, or 2.54 cm. Used for screen sizes, pipe diameters, and small hardware dimensions.
- Nautical Mile (nmi) — exactly 1,852 meters. Defined as one arc-minute of latitude; the standard unit in aviation and maritime navigation.
- Light Year (ly) — approximately 9.461 × 10¹⁵ meters. The distance light travels in one Julian year; used exclusively in astronomy.
Key Conversion Formulas
These are the exact conversion factors used by our calculator:
| From | To | Multiply by |
|---|---|---|
| Miles | Kilometers | 1.609344 |
| Kilometers | Miles | 0.621371 |
| Feet | Meters | 0.3048 (exact) |
| Meters | Feet | 3.28084 |
| Inches | Centimeters | 2.54 (exact) |
| Centimeters | Inches | 0.393701 |
| Yards | Meters | 0.9144 (exact) |
| Nautical Miles | Kilometers | 1.852 (exact) |
Common Use Cases
Travel & Navigation
If you're driving in the United States or United Kingdom, road signs show distances in miles. Most of the rest of the world uses kilometers. A quick mental shortcut: to estimate miles from km, divide by 1.6 (e.g., 80 km ÷ 1.6 = 50 miles). For the exact conversion, use our calculator above. Marathon runners frequently need this: the race is exactly 42.195 km, or 26.219 miles. A 5K race is 3.107 miles; a 10K is 6.214 miles.
Height & Body Measurements
In the US, height is expressed in feet and inches (e.g., 5 ft 11 in = 180.3 cm). In metric countries, height is given in centimeters or meters. Medical records often require both. A person who is 1.75 m tall is 5 ft 8.9 in; 6 ft converts to exactly 182.88 cm.
Property & Construction
Real estate in the US is measured in feet and square feet, while most other countries use meters and square meters. A 100 m² apartment is 1,076 sq ft. A room that's 4 m × 5 m is approximately 13.1 ft × 16.4 ft.
Screen & Product Sizes
Display screen sizes are measured diagonally in inches, regardless of the country. A 55-inch TV screen measures 139.7 cm (55 × 2.54). Monitor sizes and smartphone dimensions are also universally given in inches, making inch-to-centimeter conversion frequently needed worldwide.
Aviation & Nautical
Aviation uses feet for altitude (e.g., cruising altitude is typically 35,000 ft = 10,668 m) and nautical miles for horizontal distances. One nautical mile equals exactly 1.852 km, and one knot (the speed unit) is one nautical mile per hour.
Frequently Asked Questions
How many feet are in a meter?
One meter equals exactly 3.28084 feet, or equivalently 3 feet and 3.37 inches. The foot is defined as exactly 0.3048 meters by the international yard and pound agreement signed in 1959 by the US, UK, Australia, Canada, New Zealand, and South Africa.
How many kilometers are in a mile?
One mile equals exactly 1.609344 kilometers. This is an exact definition: the mile is defined as 5,280 feet, and the foot is 0.3048 m (exact), so 5,280 × 0.3048 = 1,609.344 m = 1.609344 km. To convert the other way: 1 km = 0.621371 miles.
How many centimeters are in an inch?
Exactly 2.54 centimeters are in one inch. This is an exact definition. To convert inches to centimeters, multiply by 2.54. To convert centimeters to inches, divide by 2.54 (or multiply by 0.393701).
What is the difference between a nautical mile and a regular mile?
A nautical mile (1,852 m) is longer than a statute mile (1,609.344 m). The nautical mile was historically defined as one arc-minute of latitude — useful for navigation since the Earth's circumference is approximately 21,600 nautical miles (360° × 60'). Aviation and maritime navigation use nautical miles; road signs and everyday distances use statute miles.
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Conversion factors sourced from NIST Handbook 44 and the International Yard and Pound Agreement (1959). Accuracy note.