Unit Converter
Convert Units
How it works
Select a category (length, weight, temperature, area, volume, speed, or time), then choose the units to convert between. Enter a value and the result updates as you type. All conversions are bidirectional: edit either field to convert in the other direction.
Every conversion factor inside the tool traces back to the SI definition of the relevant base unit. A metre is defined by the speed of light; an inch is defined as exactly 25.4 millimetres; a pound (avoirdupois) is exactly 0.453 592 37 kilograms. Conversions between metric and imperial units here are therefore not approximations: they are the exact ratios used by CIPM, NIST, and the aviation and pharmaceutical industries.
A few reference points worth keeping around: 1 metre = 3.280 84 feet; 1 kilogram = 2.204 62 pounds; 1 kilometre = 0.621 371 miles; 1 litre = 0.264 172 US gallons; 1 °C = (°F − 32) × 5/9. Temperature is the one category that is not a simple multiplier. The Celsius to Fahrenheit conversion has both an offset and a scale, while Kelvin has an offset from Celsius but no scale difference (1 K = 1 °C in size).
For time-specific conversions (minutes to days, seconds to hours, and so on) the dedicated Duration Converter is usually easier, because it shows all units at once and gives you a human-readable breakdown.
Frequently Asked Questions
What unit categories are available?
- Length, weight, temperature, area, volume, speed, and time. Each category includes the most common metric units (m, kg, km/h, m², L, …) plus their imperial counterparts (inch, pound, mph, ft², US gallon, …).
How accurate are the conversions?
- Accurate to about 15–17 significant digits, the precision of JavaScript's double-precision floating-point numbers. The underlying ratios (1 inch = 25.4 mm, 1 lb = 0.453 592 37 kg) are the exact SI definitions, so the only error is the one introduced by rounding the final decimal you see on screen.
Why is the temperature conversion different from the others?
- Because temperature scales don't start at the same zero. Going from °C to °F you multiply by 9/5 and then add 32; going from °F to °C you subtract 32 first and then multiply by 5/9. That offset is why −40 °C = −40 °F, the one point where the two scales cross.
What is the difference between a US gallon and a UK gallon?
- A US gallon is 3.785 411 784 L and a UK (imperial) gallon is 4.546 09 L, about 20% bigger. The tool exposes both, so always check which one a recipe, car spec, or fuel-economy number is using before converting.
How do I convert minutes to hours or days to minutes?
- Use the Time category here, or the standalone Duration Converter, which is usually faster: it shows milliseconds, seconds, minutes, hours, days, and weeks at the same time, and it adds a human-readable breakdown like "1 hour, 30 minutes" underneath.
Does it handle compound units like miles per hour squared?
- No, only single units are supported in each category. Compound units (m/s², Wh/km, kg·m/s) are out of scope: those conversions depend on which derived unit you want, and the safest path is to convert each base unit separately and combine them.
Common unit conversion reference
Exact conversion factors (not rounded approximations) for the cross-system conversions people look up most. All values trace back to the SI definitions published by BIPM / NIST.
| From | To | Multiply by | Example |
|---|---|---|---|
| 1 inch | centimetre | 2.54 (exact) | 10 in = 25.4 cm |
| 1 centimetre | inch | 0.393 700 787 | 100 cm = 39.37 in |
| 1 foot | metre | 0.3048 (exact) | 6 ft = 1.8288 m |
| 1 metre | foot | 3.280 839 895 | 100 m = 328.08 ft |
| 1 mile | kilometre | 1.609 344 (exact) | 60 mi = 96.56 km |
| 1 kilometre | mile | 0.621 371 192 | 100 km = 62.14 mi |
| 1 pound (lb) | kilogram | 0.453 592 37 (exact) | 150 lb = 68.04 kg |
| 1 kilogram | pound (lb) | 2.204 622 622 | 70 kg = 154.32 lb |
| 1 ounce (oz) | gram | 28.349 523 125 (exact) | 16 oz = 453.59 g |
| 1 gram | ounce | 0.035 273 962 | 100 g = 3.53 oz |
| 1 stone (UK) | kilogram | 6.350 293 18 | 10 st = 63.5 kg |
| 1 US gallon | litre | 3.785 411 784 (exact) | 10 US gal = 37.85 L |
| 1 UK gallon | litre | 4.546 09 (exact) | 10 UK gal = 45.46 L |
| 1 litre | US gallon | 0.264 172 052 | 100 L = 26.42 US gal |
| 1 fluid oz (US) | millilitre | 29.573 529 6 (exact) | 8 fl oz = 236.59 mL |
| 1 acre | square metre | 4046.856 422 4 (exact) | 1 ac = 4046.86 m² |
| 1 square foot | square metre | 0.092 903 04 (exact) | 100 sq ft = 9.29 m² |
| 1 Celsius | Fahrenheit | °F = °C × 9/5 + 32 | 20°C = 68°F |
| 1 Fahrenheit | Celsius | °C = (°F − 32) × 5/9 | 75°F = 23.89°C |
| 1 Celsius | Kelvin | K = °C + 273.15 | 0°C = 273.15 K |
| 1 mph | km/h | 1.609 344 (exact) | 60 mph = 96.56 km/h |
| 1 km/h | mph | 0.621 371 192 | 100 km/h = 62.14 mph |
| 1 knot | km/h | 1.852 (exact) | 20 kn = 37.04 km/h |
Conversions marked "(exact)" are defined by international agreement and have no rounding error. The others are irrational multipliers truncated to 9 decimal places. Beyond that, precision is limited by the floating-point representation.