Length Converter
Convert between millimeters, centimeters, meters, kilometers, inches, feet, yards, miles, nautical miles, and light years. All conversions update instantly.
| Unit | Value |
|---|---|
| Millimeter (mm) | 1000 |
| Centimeter (cm) | 100 |
| Meter (m) | 1 |
| Kilometer (km) | 0.001 |
| Inch (in) | 39.370079 |
| Foot (ft) | 3.28084 |
| Yard (yd) | 1.093613 |
| Mile (mi) | 0.000621 |
| Nautical Mile (nmi) | 0.00054 |
| Light Year (ly) | 1.057e-16 |
How to Convert Length Units
Length conversion is the process of expressing the same physical distance using a different unit of measurement. There are two major systems in everyday use: the metric system (SI) and the imperial/US customary system. Metric units use powers of 10, making conversion a matter of moving a decimal point. Imperial units use less regular ratios and require explicit multiplication or division factors.
All conversions in this tool work by first converting your input value to meters (the SI base unit for length), then converting from meters to the target unit. This two-step "base unit" method guarantees consistent results regardless of which pair of units you select.
Length Conversion Formulas
The formula structure is the same for every pair of units:
Result = Input × (From factor / To factor)
where each factor represents how many meters equal one of that unit.
| Unit | Exact value in meters | Notes |
|---|---|---|
| 1 Millimeter (mm) | 0.001 m | 1/1000 of a meter |
| 1 Centimeter (cm) | 0.01 m | 1/100 of a meter |
| 1 Meter (m) | 1 m | SI base unit |
| 1 Kilometer (km) | 1,000 m | 1,000 meters |
| 1 Inch (in) | 0.0254 m | Exact by international agreement since 1959 |
| 1 Foot (ft) | 0.3048 m | 12 inches; exact |
| 1 Yard (yd) | 0.9144 m | 3 feet; exact |
| 1 Mile (mi) | 1,609.344 m | 5,280 feet; exact |
| 1 Nautical Mile (nmi) | 1,852 m | One arc-minute of latitude |
| 1 Light Year (ly) | 9.461 × 10¹&sup5; m | Distance light travels in one year |
Common Length Conversions
The most frequent conversions involve the cm-to-inch relationship (human height, screen sizes, clothing) and the km-to-mile relationship (road distances, speed limits). Here are the key reference values to memorize:
| Conversion | Exact factor | Quick approximation |
|---|---|---|
| 1 inch → cm | 2.54 cm | 2.5 cm (within 2%) |
| 1 cm → inches | 0.39370 in | 0.4 in |
| 1 foot → meters | 0.3048 m | 0.3 m |
| 1 meter → feet | 3.28084 ft | 3.28 ft |
| 1 mile → km | 1.60934 km | 1.6 km |
| 1 km → miles | 0.62137 mi | 0.62 mi |
| 1 yard → meters | 0.9144 m | ~0.9 m |
Metric vs. Imperial: Which System to Use?
The metric system is used by virtually every country in the world for science, engineering, and most everyday measurements. The United States is the main holdout for everyday use, still using miles, feet, and inches for most consumer contexts. The UK uses a hybrid: kilometers for EU-facing contexts, miles for road distances, and centimeters/meters for most other measurements.
For scientific work, always use SI units. For construction in the US, feet and inches remain standard. For international trade and engineering, metric is required by ISO standards.
Frequently Asked Questions
How many centimeters are in an inch?
One inch equals exactly 2.54 centimeters. This is a defined (exact) conversion: 1 in = 2.54 cm. Therefore 1 cm = 1/2.54 in ≈ 0.3937 inches.
How do I convert feet to meters?
One foot equals 0.3048 meters (exact). To convert feet to meters, multiply by 0.3048. To convert meters to feet, divide by 0.3048 (or multiply by 3.28084). Example: 6 ft = 6 × 0.3048 = 1.8288 m.
How many miles are in a kilometer?
1 kilometer = 0.621371 miles. 1 mile = 1.60934 km. A quick approximation: multiply km by 0.6 to get a rough miles figure. Example: 10 km ≈ 6.21 miles.
What is a nautical mile and how does it differ from a land mile?
A nautical mile is exactly 1,852 meters (1.852 km), while a statute (land) mile is 1,609.344 meters. A nautical mile corresponds to one arc-minute of latitude, making it natural for navigation. 1 nautical mile = 1.15078 statute miles.
How far is a light year in kilometers?
A light year is the distance light travels in one year: approximately 9.461 × 10¹² km (9.461 trillion km, or about 5.879 trillion miles). It is a unit of distance, not time.
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