Unit Converter
Pick a category, choose two units and type — the conversion runs in both directions as you go, with exact factors and a quick reference table for each category.
📂 Category
📏 🔄 Convert
📋 Quick reference
| From | To |
|---|---|
| 1 in | 2.54 cm |
| 1 ft | 0.3048 m |
| 1 yd | 0.9144 m |
| 1 mi | 1.609344 km |
| 1 km | 0.621371 mi |
| 1 nmi | 1.852 km |
| 100 m | 328.08399 ft |
How to use the unit converter
- Choose a category — length, mass, temperature, volume, area, speed, time, digital storage, pressure, energy or fuel economy.
- Pick the unit you are converting from and the unit you want to.
- Type a number in either box. The other side updates immediately, so you can work in whichever direction suits you.
- Press ↔ Swap to flip the two units without retyping anything.
- Set the decimal places you want, or leave it on Auto for a sensible default.
Your last category is remembered for the next visit, and every calculation happens in your browser.
How it works
Most categories are linear: each unit records how many base units it is worth, and a conversion is one multiplication and one division.
result = value × factor(from) / factor(to)For length the base is the metre, for mass the kilogram, for volume the litre. Where an exact legal definition exists, that exact number is used rather than a rounded approximation:
| Conversion | Exact factor | Rounded |
|---|---|---|
| 1 inch | 0.0254 m | 2.54 cm |
| 1 foot | 0.3048 m | 30.48 cm |
| 1 mile | 1609.344 m | 1.609 km |
| 1 pound | 0.45359237 kg | 453.6 g |
| 1 US gallon | 3.785411784 L | 3.785 L |
| 1 imperial gallon | 4.54609 L | 4.546 L |
| 1 acre | 4046.8564224 m² | 0.4047 ha |
Two categories cannot work that way and get their own converters.
Temperature scales have different zero points, so every conversion goes through Celsius:
°C = (°F − 32) × 5/9 °F = °C × 9/5 + 32
K = °C + 273.15 °R = (°C + 273.15) × 9/5That is why 100 °C is 212 °F but 200 °C is not 424 °F. The tool also warns you if you enter a temperature below absolute zero.
Fuel economy units are reciprocals of each other. Miles per gallon measures distance per unit of fuel, while litres per 100 km measures fuel per unit of distance, so one goes up as the other goes down:
L/100 km = 235.215 / mpg (US)
L/100 km = 282.481 / mpg (imperial)Worked examples
Length. A 5 km run is 3.107 miles. A 6-foot doorway is 1.829 m. A 42.195 km marathon is 26.219 miles.
Weight. A 12-stone person weighs 76.2 kg or 168 lb. A 250 g pack of butter is 8.82 oz, and a US short ton is 907.18 kg.
Temperature. An oven at 180 °C is 356 °F. Body temperature of 98.6 °F is 37 °C. A −40 reading is the same number on both scales, which is the only place they meet.
Volume. A US cup is 236.6 mL, an imperial pint is 568.3 mL and a US pint is only 473.2 mL — worth knowing when following a recipe from the other side of the Atlantic.
Speed. 60 mph is 96.56 km/h; a 100 km/h motorway limit is 62.14 mph; one knot is 1.852 km/h by definition.
Digital storage. A drive sold as 1 TB holds 1,000,000,000,000 bytes, which your operating system may display as 931 GiB. A gibibyte is 1,073,741,824 bytes, about 7.4% more than a gigabyte.
Pressure. A tyre inflated to 32 psi is at 2.21 bar or 221 kPa. Standard atmospheric pressure is 1013.25 hPa, which weather reports usually round to 1013 mb.
Energy. 1 kWh is 3.6 MJ or about 860 food calories. A 2,000 kcal daily diet is roughly 8.4 MJ.
Fuel economy. A car rated at 30 mpg (US) uses about 7.84 L/100 km. The same car would be advertised as 36 mpg in the UK, because an imperial gallon is larger.
Tips and common mistakes
- Check which gallon, pint or ton you mean. US and imperial units share names but not sizes, and US tons, UK tons and metric tonnes are three different things.
- Do not add temperature differences using the conversion formula. A rise of 10 °C is a rise of 18 °F, not 50 °F — for differences, use the ratio 9/5 alone.
- Watch decimal versus binary storage units. kB, MB and GB are powers of 1,000; KiB, MiB and GiB are powers of 1,024.
- Squared and cubed units scale differently. Doubling a length quadruples the area and multiplies the volume by eight, so a square foot is 0.0929 m², not 0.3048.
- Higher is better for mpg, lower is better for L/100 km. Comparing the two directly without converting is the classic fuel-economy mistake.
- Round only at the end. Converting through an intermediate unit and rounding each time compounds the error.
Results are calculated from published definitions and are accurate for everyday use, but rounding at the precision you choose means they are estimates rather than certified measurements.
Glossary
- Base unit – the reference unit a category is measured against internally, such as the metre or the kilogram.
- Conversion factor – how many base units one unit is worth.
- Imperial – the British system defined in 1824, still used for road distances and beer in the UK.
- US customary – the American system, which shares names with imperial but uses different volume units.
- Absolute zero – −273.15 °C, the lowest possible temperature and the zero of the Kelvin and Rankine scales.
Frequently asked questions
How many kilometres are in a mile?
Exactly 1.609344 km. The international mile has been defined from the metre since 1959, so this is a definition rather than a measurement, and 1 km is 0.621371 miles.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32, so 100 °C is 212 °F and 20 °C is 68 °F. Temperature scales have different zero points, which is why you cannot convert them with a single multiplier the way you can with length or mass.
Why are US and imperial gallons different?
The US gallon comes from the old English wine gallon of 231 cubic inches, which is 3.785411784 L, while the imperial gallon was redefined in 1824 as 4.54609 L. An imperial gallon is about 20% larger, and the same applies to pints and fluid ounces.
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure, so 30 mpg is about 7.84 L/100 km. For imperial mpg, divide 282.481 instead. The two scales run in opposite directions — higher mpg is better, lower L/100 km is better.
Why does my 1 TB drive show as 931 GB?
The manufacturer counts 1 TB as 1,000,000,000,000 bytes, while the operating system divides by 1,024 three times and calls the result a gigabyte. The same bytes are 1,000 GB in decimal units or 931 GiB in binary ones.
How many decimal places should I use?
Use the precision selector. Two or three decimals are enough for everyday conversions; keep more when a small unit is being converted to a large one, or when you need the exact defining factor.
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