Unit Converters

Unit conversion looks like the most mechanical thing on this site, and it's where some of the most expensive mistakes happen. The recurring theme is that a unit name doesn't always identify a unit.

The gallon isn't one unit

A US gallon is about 3.785 liters and an imperial gallon is about 4.546 liters, a difference of roughly twenty percent. Fluid ounces diverge too, and confusingly in the opposite direction, since an imperial fluid ounce is slightly smaller than a US one despite the imperial gallon being larger. Recipes, fuel figures and shipping volumes crossing between the United States and the United Kingdom need the specific variant named, not just the word gallon. Tons have the same problem three ways, with a short ton, a long ton and a metric tonne all in active use.

Why your hard drive looks smaller than advertised

Storage manufacturers use decimal prefixes, so a terabyte means a trillion bytes. Operating systems have traditionally reported using binary multiples of 1,024, which are properly called kibibytes, mebibytes and gibibytes. The gap compounds with scale, reaching about seven percent at the terabyte level. A drive sold as one terabyte shows up as roughly 931 of what the system calls gigabytes. Neither figure is wrong, they are different units wearing similar names.

Temperature doesn't convert like the others

Every other converter here scales by a factor, so half the input gives half the output. Temperature scales have an offset as well. That breaks the intuition in a specific way: you cannot convert a temperature difference using the same formula you use for a temperature.

A reading of 10 °C is 50 °F, but a rise of 10 °C is a rise of 18 °F, not 50. The offset applies to positions on the scale and not to intervals between them. Anyone converting a tolerance, a daily range, or a rate of change needs the factor alone, which is why specification sheets state temperature ranges and temperature deltas in separate rows.

A final habit worth keeping: convert once, at the end. Chaining conversions through an intermediate unit compounds rounding at every step, and the drift becomes visible in engineering and dosage contexts where the final digit matters.