Unit converter

How the conversion works

Each unit is stored as an exact multiple of one base unit (metres, kilograms, square metres, litres or metres per second). To convert, the value is multiplied into the base unit and then divided by the target unit's factor. Temperature is different because the scales do not start at the same zero, so it uses formulas instead.

Temperature formulas

°C = (°F − 32) × 5 ÷ 9
°F = °C × 9 ÷ 5 + 32
K = °C + 273.15

Values below absolute zero (0 K, −273.15 °C, −459.67 °F) are rejected because they cannot exist.

Worked examples

• 100 °F to °C: (100 − 32) × 5 ÷ 9 = 37.78 °C.
• 5 km to miles: 5,000 m ÷ 1,609.344 m = 3.107 miles.
• 10 kg to pounds: 10 ÷ 0.45359237 = 22.046 lb.
• 1 UK gallon to US gallons: 4.54609 L ÷ 3.785411784 L = 1.201 US gallons.

The exact factors used

Unit	Defined as
Inch	25.4 mm exactly (so a foot is 0.3048 m, a yard 0.9144 m)
Mile	1,609.344 m
Nautical mile	1,852 m; a knot is one nautical mile per hour
Pound (lb)	0.45359237 kg exactly; an ounce is 1/16 lb, a stone 14 lb
Acre	4,046.8564224 m²; a hectare is 10,000 m²
US gallon	231 cubic inches = 3.785411784 L
UK (imperial) gallon	4.54609 L exactly
US cup / fl oz / tbsp / tsp	1/16 gallon / 1/128 gallon / 1/2 fl oz / 1/3 tbsp

The inch, foot, yard, mile and pound values come from the 1959 international yard and pound agreement, used by the US, UK and Commonwealth countries.

FAQ

Why are US and UK gallons different?

They come from different historical definitions. The UK gallon is about 20% larger, and US and UK fluid ounces and pints also differ. This converter uses US units for cups, spoons and fluid ounces.

Is weight the same as mass?

Strictly, kilograms and pounds measure mass. In everyday use, including on scales, "weight" means the same thing, so they are treated as one here.

How many decimals are shown?

Up to 8 significant figures, which is more than enough for most uses. The calculation itself uses full precision.