Unit Converter

The ones that can be, yes. Since 1959 the inch is defined as exactly 25.4 millimetres and the pound as exactly 0.45359237 kilograms, and every other imperial length and weight follows by whole-number ratios, so those factors are exact rather than rounded. The exceptions are marked: pressures involving mercury or the atmosphere, and the BTU, are defined against physical quantities that do not divide evenly.

Because they were never the same. A US pint is 16 US fluid ounces and an imperial pint is 20 imperial fluid ounces, making the imperial pint about 20 percent larger. Both are listed separately and labelled, because a recipe that says pint without saying which is a recipe that will go wrong somewhere.

A US cup is 236.588 millilitres. A metric cup, standard in Australia and New Zealand, is 250. A British recipe will usually give weights instead, which is one reason British baking travels better than American baking does.

Because two definitions of a gigabyte are in play and both are defensible. The manufacturer counts a terabyte as a million million bytes, following the SI prefixes. The operating system divides by 1,024 three times, the binary convention, while still writing GB. The correct name for the binary unit is the gibibyte, standardised by the IEC in 1998 and used by almost nobody. Nothing is missing from the drive.

Because the scales disagree about two things rather than one. Their degrees are different sizes, and their zero points are in different places, so the conversion needs an offset as well as a scale factor. Applying them in the wrong order is wrong by about 18 degrees. Minus forty is the same number on both scales, which is a quick way to check any conversion.