Length Converter
Length Conversion — Metric, Imperial, and More
Length conversions are needed constantly — reading a blueprint in metric when you think in feet, comparing running distances across countries, understanding international paper sizes, or interpreting a product spec sheet from overseas. This converter covers the full range from millimeters to miles in a single calculation.
Key Conversion Factors
Real-World Example
The default input is 1 meter, which converts to:
- Feet: 3.281 ft
- Inches: 39.37 in
- Centimeters: 100 cm
- Millimeters: 1,000 mm
- Yards: 1.094 yd
- Kilometers: 0.001 km
- Miles: 0.000621 mi
The Metric System — Built for Conversion
Metric length is based on the meter with prefixes that are exact powers of 10:
- Millimeter (mm) = 0.001 m — engineering tolerances, rainfall, screen dimensions
- Centimeter (cm) = 0.01 m — human dimensions, clothing sizes, small measurements
- Meter (m) = base unit — room dimensions, height, sports distances
- Kilometer (km) = 1,000 m — road distances, geographic distances
Converting within metric is just moving the decimal point — 1,500 mm = 150 cm = 1.5 m = 0.0015 km. No multiplication required.
The Imperial System — Inches, Feet, Yards, Miles
The imperial length system has no logical internal structure — 12 inches per foot, 3 feet per yard, 1,760 yards per mile. These conversion factors are historical and arbitrary, which is why mental math is harder across imperial units than metric.
- Inch (in) — small measurements, screen sizes, hardware, lumber dimensions
- Foot (ft) — room dimensions, height (in the US), elevation
- Yard (yd) — fabric, American football, golf, some gardening
- Mile (mi) — road distances in the US and UK
What Is a Nautical Mile?
A nautical mile (1,852 meters / 1.151 statute miles) is used in aviation and maritime navigation worldwide, regardless of whether a country uses metric or imperial. It's based on the Earth's geometry: one nautical mile equals one minute of arc of latitude (1/60 of a degree). This makes it intrinsically linked to geographic coordinates, which is why navigators prefer it — a vessel traveling 60 nautical miles north moves exactly 1 degree of latitude.
Quick Mental Conversion Shortcuts
- km to miles: multiply by 0.6 (rough). 10 km ≈ 6 miles (actual: 6.21)
- miles to km: multiply by 1.6. 5 miles ≈ 8 km (actual: 8.05)
- cm to inches: divide by 2.54, or multiply by 0.4. 10 cm ≈ 4 in (actual: 3.94)
- meters to feet: multiply by 3.3. 2m ≈ 6.6 ft (actual: 6.56)
Frequently Asked Questions
How long is a 5K in miles?
5 kilometers = 3.107 miles. A 10K is 6.214 miles. A half marathon (21.1 km) is 13.11 miles. A full marathon (42.195 km) is 26.219 miles. These conversions come up so often for runners that they're worth memorizing — or bookmarking this converter.
What is the difference between a UK mile and a US mile?
They are the same. Both the US and UK define a statute mile as exactly 5,280 feet or 1,609.344 meters. The "international mile" standardized this in 1959. The only historical variant is the "nautical mile" (1,852 m) used in navigation, which is different from the statute mile.
How do I convert height from cm to feet and inches?
Divide centimeters by 30.48 to get feet (with a decimal). The whole number is your feet; multiply the decimal by 12 to get remaining inches. For example: 175 cm ÷ 30.48 = 5.741 feet → 5 feet + (0.741 × 12) = 5 feet 8.9 inches → 5'9". The calculator handles this automatically — just enter your height in cm and read the feet and inches result.
Why does the US still use imperial measurements?
The US is one of only three countries (along with Liberia and Myanmar) that hasn't officially adopted the metric system for everyday use. Attempts to convert have repeatedly stalled due to the massive cost of converting infrastructure, signage, and tooling, plus the cultural resistance to changing intuitive reference points people have used their whole lives. Science, medicine, and military in the US use metric; everyday life remains largely imperial.
How is a meter officially defined?
Since 1983, the meter is defined as the distance light travels in a vacuum in exactly 1/299,792,458 of a second. This is an invariant physical constant — the meter is now defined by the speed of light rather than any physical artifact. The original 1793 definition was 1/10,000,000 of the distance from the equator to the North Pole along a meridian through Paris.