Unit Converter
Length, weight, temperature, volume and more.
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All unit convertersQuestions
Are these conversions exact or approximate?
Exact, wherever an exact definition exists — which is most of them. The 1959 international yard and pound agreement fixed the inch at exactly 25.4 mm and the pound at exactly 0.45359237 kg, so every length, mass, area and volume conversion derived from those is exact rather than measured. Results are shown to seven significant figures.
Why is temperature handled differently?
Because Celsius, Fahrenheit and kelvin do not share a zero point. Every other dimension passes through zero at the same place, so a single multiplication works. Temperature needs both a scale and an offset, which is also why a 10-degree difference does not convert the same way a 10-degree reading does.
Is a kilobyte 1,000 bytes or 1,024?
Both definitions are in use, which is why this converter offers each separately. A kilobyte is 1,000 bytes under the SI definition that storage manufacturers and networking use; a kibibyte is exactly 1,024. The IEC standardised the binary prefixes — kibi, mebi, gibi — in 1998 to end the ambiguity, but adoption has been patchy, and the gap compounds to about 10% by the time you reach terabytes.
US or imperial gallons?
Both are available and they are listed separately, because the difference is large: an imperial gallon is about 20% bigger than a US gallon. The same caution applies to fluid ounces, pints and cups. If a source does not say which system it means, fuel-economy and recipe figures can be wrong by a fifth without looking obviously wrong.
Does this work offline?
Yes. Every conversion is arithmetic performed in your browser — nothing is sent to a server, there is no lookup and no API call. Once the page has loaded you can disconnect entirely and it keeps working.
About unit converter
What this covers
| Dimension | Units |
|---|---|
| Length | km, m, cm, mm, mi, ft, in, yd, nmi |
| Weight & mass | kg, g, lb, oz, t, mg, st |
| Temperature | °C, °F, K |
| Volume | L, mL, gal, fl oz, cup, m³, gal (UK), pt, tbsp, tsp |
| Area | m², ft², acre, ha, km², mi², in² |
| Speed | km/h, mph, m/s, kn, ft/s |
| Data size | KB, MB, GB, TB, MiB, GiB, B, KiB, TiB |
| Pressure | bar, psi, kPa, atm, mmHg, Pa |
The conversions are exact, not approximate
Most people assume metric-to-imperial conversion is inherently fuzzy. It is not. The international yard and pound agreement of 1959 defined the inch as exactly 25.4 millimetres and the pound as exactly 0.45359237 kilograms. Every length, mass, area and volume relationship between the two systems descends from those two definitions, so a mile is exactly 1,609.344 metres — not approximately.
The nautical mile (exactly 1,852 m), the US gallon (exactly 231 cubic inches) and the acre (exactly 4,840 square yards) are likewise defined rather than measured. The only imprecision here is how many digits you choose to keep.
Three places conversions go wrong
Temperature differences are not temperatures
Converting 10 °C gives 50 °F, but a rise of 10 °C is a rise of 18 °F. The offset applies to a point on the scale, not to an interval. For differences, use only the scaling part and leave the +32 out. This is the most common temperature error there is.
US and imperial measures share names but not sizes
An imperial gallon is about 20% larger than a US gallon. An imperial pint is 20 fluid ounces against the US 16. Cups are worse: US customary is about 237 mL, US legal is 240, metric is 250, Japanese is 200 — and recipes almost never specify. When a figure is only 20% out, it looks plausible, which is exactly what makes it dangerous.
Kilobytes are two different units
A kilobyte is 1,000 bytes under the SI definition used by storage manufacturers and networking. A kibibyte is exactly 1,024. The gap compounds at every step, reaching about 10% by the terabyte — which is the entire explanation for why a 1 TB drive displays as 931 GB. Nothing is missing; the units differ. Both are offered here separately.
Why the answers are not all rounded to two decimals
Fixed decimal places break across the range a general converter has to cover. Two decimals turns 0.0006 miles into “0.00”; twelve turns 25.4 millimetres into noise. Results here use significant figures instead, so small numbers keep their detail and large ones stay readable — and trailing zeros are trimmed, so exact results read as exact.
One practical habit: round at the end, not partway through. Rounding an input before converting introduces an error that the conversion then multiplies.
Popular conversions
km to miles, miles to km, kg to pounds, pounds to kg, Celsius to Fahrenheit, Fahrenheit to Celsius, cm to inches, inches to cm, litres to gallons, GB to MB.