How it works
Every unit is converted through one base unit for its category — metres for length, kilograms for weight, litres for volume, square metres for area, metres per second for speed, bytes for data and seconds for time. The value is multiplied by the “from” factor and divided by the “to” factor:
result = value × factor(from) ÷ factor(to)The factors are exact by international definition wherever one exists. Since 1959 the inch is exactly 2.54 cm, the foot 0.3048 m, the mile 1,609.344 m and the pound exactly 0.45359237 kg.
Worked example. 6 feet in metres: 6 × 0.3048 = 1.8288 m. 1 mile in kilometres: 1 × 1,609.344 ÷ 1,000 = 1.609344 km. 1 kg in pounds: 1 ÷ 0.45359237 = 2.20462262185 lb.
Temperature is different
Temperature scales have different zero points, so they cannot be converted with a single factor:
°F = °C × 9 ÷ 5 + 32 · K = °C + 273.15Body temperature 37 °C = 37 × 9 ÷ 5 + 32 = 98.6 °F. Values below absolute zero (−273.15 °C) are rejected.
Data sizes: KB or KiB?
Storage makers use decimal prefixes (1 GB = 1,000,000,000 bytes), while many operating systems count in binary units (1 GiB = 1,073,741,824 bytes). That is why a “500 GB” drive appears as about 465 GiB. Both are available here.
US and UK measures
Cups, pints, quarts and gallons here are US customary measures (1 US gallon = 3.785411784 L). The UK (imperial) gallon is larger — 4.54609 L — and is listed separately. Months and years in the time category are average Gregorian lengths (a year of 365.2425 days); for calendar dates use the date calculator.
Results are shown with up to 10 significant digits, so tiny floating-point artefacts never appear. For body measurements, the BMI calculator converts pounds and inches for you.