Unit converters

The number is rarely the hard part

Arithmetic is not what makes a conversion go wrong. Multiplying by 2.54 is not difficult, and a search engine will do it inline before a page has finished loading. What goes wrong is the unit: a recipe that says "one cup" without saying whose cup, a pressure quoted without saying whether it is measured against a vacuum or against the air in the room, a drive sold in one definition of a gigabyte and reported by the operating system in another. In each case both parties are converting correctly and still disagree, because they are not converting the same quantity.

That is the test each converter here has to pass to earn a page. Where a conversion carries a real ambiguity, a domain convention or a trap worth warning about, it gets several hundred words explaining it. Where it is a single unambiguous multiplication, it gets a working tool and no essay, because padding it would waste the reader's time and would not make the answer any more correct. The converters listed above are the ones with something to say.

All of them run on your own device: the figure you type is never sent anywhere, which matters more than it sounds when the number is a body weight, a salary or a medical dose. Each page carries the formula it uses, so the arithmetic can be checked rather than trusted, along with a table of common values for anyone who came to read a number rather than type one.