Unit Converter

Unit conversion is the arithmetic nobody wants to do twice. Whether it is a recipe in cups, a parcel weight in pounds, a running distance in kilometres or a disk quota in gibibytes, the answer matters and the working is tedious.

The factors here are the exact defined values rather than the rounded ones that circulate. An inch is defined as exactly 25.4 millimetres and a pound as exactly 0.45359237 kilograms; using 2.54 and 0.454 introduces drift that shows up as soon as you convert something large or convert twice.

Temperature is handled separately from everything else, because it has offsets as well as scales. Converting it with a simple multiplication — the way length or weight works — would put 0 °C at 0 °F, which is a mistake that looks plausible right up until you check it.

Storage has two conflicting conventions. Drive manufacturers use decimal units where a gigabyte is 1,000,000,000 bytes, while operating systems have traditionally used binary units where a gibibyte is 1,073,741,824 bytes — about 7% more.

That is why a 1 TB drive shows as roughly 931 GB in a file manager. Nothing is missing; the two numbers are the same quantity measured with different-sized units. Both are offered here so you can see the difference directly.