📏 Length Unit Converter
How It Works
Type in any field and the other seven update instantly, to six decimal places. The conversions are exact by definition, not approximation: since the 1959 international yard agreement, 1 inch ≡ 2.54 cm exactly — which makes 1 foot exactly 30.48 cm and 1 mile exactly 1,609.344 m.
- 1 km = 1,000 m; 1 m = 100 cm = 1,000 mm
- 1 ft = 12 in; 1 yd = 3 ft; 1 mile = 1,760 yd
Rules of Thumb for Travelers
- Miles → km: multiply by 1.6. A 60 mph speed limit is about 97 km/h; 100 miles is about 160 km. Going the other way, multiply km by 0.62.
- A marathon is 42.195 km = 26.2 miles — handy for calibrating what "a long way" means in either unit.
- Feet for altitude: aviation worldwide uses feet. Cruising at 35,000 ft is about 10,700 m.
- Height in profiles: convert ft'in" to cm by turning everything into inches first (feet × 12 + inches), then × 2.54. So 5'10" = 70 in = 177.8 cm.
| cm | 150 | 155 | 160 | 165 | 170 | 175 | 180 | 185 | 190 |
|---|---|---|---|---|---|---|---|---|---|
| ft/in | 4'11" | 5'1" | 5'3" | 5'5" | 5'7" | 5'9" | 5'11" | 6'1" | 6'3" |
Two Feet, One Inch: Definition Trivia That Bites
- The US survey foot is gone: until 2022 the US had two slightly different feet — the international foot (0.3048 m) and the survey foot (0.30480061 m). The difference sounds absurdly small, but over a state-wide coordinate grid it amounted to meters of error, so NIST retired the survey foot. Old land-survey data may still use it.
- Screen "inches" are diagonal: a 15.6-inch laptop display measures 39.6 cm corner to corner, not across. Same diagonal with a different aspect ratio means a different area.
- A nautical mile (1,852 m) is one arc-minute of latitude — which is why ships and planes still use it: distance and coordinates line up neatly.
Frequently Asked Questions
Why does the converter give 0.999998 instead of 1 sometimes?
Round-tripping through a base unit with 6-decimal display can round the last digit. The underlying ratios are exact; take the displayed value as correct to ±0.000001.
Which countries still use miles on roads?
Chiefly the US and UK (plus a few territories). Nearly everywhere else signs distances in kilometers — including Ireland, which switched in 2005.
Is a yard close enough to a meter?
For rough talk, yes — 1 yd = 0.9144 m, about 9% short. Over a football field the gap is nearly 8.5 meters, so don't mix them in anything that gets built.
Can I enter decimals or very small values?
Yes. Tiny results below 0.0001 switch to significant-figure display (e.g. 1 mm in miles shows 6.21371e-7) so they don't collapse to zero.