At a glance
| Categories | Length, weight, temperature, area, volume, speed and data |
|---|---|
| Length units | m, km, cm, mm, mi, yd, ft, in |
| Data units | B, KB, MB, GB, TB and bits |
| Both ways | Type in either box and the other follows |
| Where it runs | Entirely in your browser — no file is uploaded to a server |
| Price | Free, with no account and no sign-up |
| Offline | Works with no connection after the first visit |
The gallon that is two different volumes
A US gallon is 3.785 litres; an imperial gallon is 4.546. That is a 20% difference, and it silently wrecks fuel-economy comparisons, recipes and any calculation copied from the wrong side of the Atlantic. Pints and fluid ounces differ too, in the opposite direction — a US pint is smaller, a US fluid ounce slightly larger.
Both are offered separately here rather than under one "gallon", because guessing which one someone meant is how the error propagates.
Weight and mass, and the tonnes
Everyday use treats kilograms and pounds as the same kind of thing, and for anything on earth that is fine. Where it matters: a metric tonne is 1,000 kg, a US short ton is about 907 kg, and a UK long ton about 1,016 kg. Shipping quotes given in "tons" are worth clarifying.
Temperature is not a ratio
Doubling 10°C does not give 20°C worth of heat, because the Celsius zero is arbitrary. Conversions between scales need the offset, not just a factor — which is why a "temperature difference" of 10 degrees converts differently from a temperature of 10 degrees.
Frequently asked questions
Which gallon should I use?
US if the source is American, imperial if British. They differ by 20%, which is enough to ruin a fuel-economy comparison or a recipe.
Is a ton the same as a tonne?
No. A metric tonne is 1,000 kg, a US short ton about 907, a UK long ton about 1,016. Worth clarifying on any shipping quote.
Why can I not just scale a temperature?
Because zero is arbitrary on Celsius and Fahrenheit. Converting needs an offset as well as a factor, and a difference converts differently from a value.
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