Unit converter

Why there are two kinds of mile

The inch, foot, yard and mile you learned in school (the "statute mile", 1609.344 m) are the same in the US and the UK — they were standardized internationally in 1959. The nautical mile (1852 m exactly) is a different, older unit still used in aviation and at sea, based on one minute of latitude. Mixing the two up is a common source of errors, so this converter keeps them separate.

US and UK volume units are not the same

Unlike length, US customary and UK imperial volume units genuinely differ: a US gallon (3.785 L) is smaller than a UK/imperial gallon (4.546 L), and the same goes for fluid ounces, pints and quarts. This converter keeps the US and UK versions of each as separate units so you don't accidentally mix them.

Why temperature is different from every other unit

Metres, pounds and gallons all start from the same zero, so converting is just multiplication. Temperature scales don't: 0 °C equals 32 °F, not 0 °F, so the conversion needs a formula (°F = °C × 9/5 + 32) rather than a single factor. Handy anchor points: water freezes at 0 °C / 32 °F, boils at 100 °C / 212 °F, and −40 is the one temperature where Celsius and Fahrenheit agree. Kelvin (science) and Rankine (US engineering) are included too — both start at absolute zero.

Calories on food labels are actually kilocalories

The "Calorie" on a food label (capital C, also written kcal) is 1000 small calories — so a 500-Calorie meal is 500 kcal, which is about 2092 kJ. European labels usually print both. The energy category here uses the thermochemical calorie (1 cal = 4.184 J exactly) and also covers Wh/kWh (electricity bills) and BTU (heating and air conditioning).

Why your hard drive looks smaller than the box said

Storage manufacturers use decimal prefixes (1 KB = 1000 bytes, ×1000 per step), while operating systems traditionally report binary ones (1 KiB = 1024 bytes, ×1024 per step). A "1 TB" drive is 1,000,000,000,000 bytes, but your OS may show it as about 931 GiB — nothing is missing, they're just different units. This converter keeps KB/MB/GB (decimal) and KiB/MiB/GiB (binary) as separate, distinct units instead of treating "MB" and "MiB" as interchangeable.

The conversions people get wrong

Most conversion mistakes are not arithmetic — they come from picking the wrong unit that happens to share a name. This converter keeps those apart deliberately, and the list of traps is short enough to remember: two kinds of mile, US and UK volumes that genuinely differ, a food Calorie that is really a kilocalorie, and storage sold in decimal units but reported by your computer in binary ones. When a number looks a few percent off, the unit is usually the culprit rather than the maths.

Cooking and shopping across borders

American recipes measure by volume where European ones measure by weight, and the two only line up if you know the ingredient — a cup of flour and a cup of water do not weigh the same. Convert the volumes here and use a scale for dry goods. Watch which pint you are reading: a US pint is 473 ml and a UK pint 568 ml, and the same gap applies to fluid ounces and quarts. Oven temperatures need the temperature category rather than a factor, because those scales do not share a zero.

Reading a spec sheet

Datasheets mix systems freely, especially for anything sold in more than one market: a tool with a metric shank quoted in inches, a pressure in bar beside a rating in psi, a weight in pounds next to a capacity in litres. Convert everything into one system before you compare two products, and watch for values that were rounded before they reached you — a stated 4 inches may be exactly 101.6 mm or a rounded 100 mm, and on a fit that difference decides whether the part goes together.