Unit Converters
These 8 unit converters cover length, weight, area, volume, speed, temperature, angle and data size. Each states which conversion factors are exact by definition and which are approximations, because several common ones are not what people assume.
8 tools
- Angle ConverterThe angle converter moves between degrees, radians, gradians, turns, arcminutes, arcseconds and NATO mils, with every conversion shown to full precision.
- Area ConverterConvert between 10 area units including hectares and acres, with the exact metric definitions.
- Data ConverterConvert data sizes across both decimal and binary prefixes, which is why your drive looks smaller than advertised.
- Length ConverterConvert between 12 length units, from nanometres to light years, using exact 1959 definitions.
- Speed ConverterConvert between km/h, mph, knots, m/s, ft/s, Mach and the speed of light.
- Temperature ConverterThe temperature converter moves between Celsius, Fahrenheit, Kelvin and Rankine, and refuses any value below absolute zero rather than returning nonsense.
- Volume ConverterConvert between 13 volume units, keeping US and Imperial measures separate as they genuinely are.
- Weight ConverterThe weight converter moves between metric and imperial mass units, and distinguishes the US short ton from the UK long ton, which differ by about 12 percent.
Exact factors and the ones people get wrong
Most of these conversions are exact by definition rather than measured. One inch is defined as exactly 25.4 millimetres, which makes every length conversion between metric and imperial exact. One pound is defined as exactly 0.45359237 kilograms. Where a factor is exact, the converter says so rather than presenting a rounded figure as the truth.
Volume is where the assumptions break down. A US fluid ounce is 29.57 millilitres and an Imperial fluid ounce is 28.41, so the Imperial pint is larger even though its ounces are smaller: it contains 20 of them where a US pint has 16. A cup is 250 millilitres only in Australia, and the converter lists each definition separately rather than picking one.
Data size carries the same trap in a different form. A megabyte is 1,000,000 bytes in decimal and 1,048,576 in binary, which is properly called a mebibyte. Drive manufacturers use the decimal figure and operating systems often use the binary one, which is why a 500 GB drive shows as roughly 465 GB.
Temperature is the only one of the eight that is not a simple multiplication, because the scales have different zero points. The converter refuses any value below absolute zero rather than returning a number that cannot exist.
Which converter covers which quantity
Each of the eight covers one physical quantity, and three of them carry a definition trap worth knowing before you rely on the result.
| The quantity | What to watch for |
|---|---|
| Length | Exact throughout. One inch is defined as 25.4 mm, so nothing here is rounded |
| Weight | Exact, but the US short ton and the UK long ton differ by about 12 percent |
| Volume | US and Imperial ounces, pints and gallons all differ. Each is listed separately |
| Data size | Decimal MB and binary MiB differ by about 5 percent, growing at each step |
| Temperature | Offset scales rather than factors. Values below absolute zero are refused |
| Speed, area and angle | Exact factors, including NATO mils alongside degrees and radians |
Frequently asked questions
Are these conversion factors exact or rounded?
Exact wherever an exact definition exists, which covers length, weight, area, speed and angle. One inch is defined as 25.4 millimetres rather than measured, so the conversion carries no error at all. Results are rounded only for display, and each page says which case applies.
Why is a UK pint bigger than a US pint if its ounces are smaller?
Because the two systems count differently. An Imperial fluid ounce is 28.41 millilitres against the US 29.57, so the ounce is smaller. An Imperial pint contains 20 of them while a US pint contains 16, which makes the Imperial pint about 20 percent larger despite the smaller unit.
Why does my 500 GB drive show as 465 GB?
Because the manufacturer counted in decimal gigabytes of 1,000,000,000 bytes and the operating system displays binary gibibytes of 1,073,741,824. The drive holds exactly what was advertised. The gap is about 7 percent at this scale and widens with every step up the units.
Is a cup 250 millilitres?
Only in Australia. A US legal cup is 240 millilitres, a US customary cup is about 236.6, and a UK cup in older recipes is 284. The converter lists each definition rather than choosing one, because a recipe that does not say which it means cannot be converted reliably.