Unit Converter
CalculatorsLength, weight, temperature, volume, area and speed, converted by exact definition — US and UK units kept apart.
Length in mi
26.21875746
42.195 km = 26.21875746 mi
km × 0.621371192237 = mi
42.195 km in every unit
- Millimetre42,195,000 mm
- Centimetre4,219,500 cm
- Metre42,195 m
- Kilometre42.195 km
- Inch1,661,220.472 in
- Foot138,435.0394 ft
- Yard46,145.01312 yd
- Mile26.21875746 mi
- Nautical mile22.78347732 nmi
How this is calculated
result = value × (size of the "from" unit ÷ size of the "to" unit) Exact by definition: 1 inch = 2.54 cm 1 pound = 0.45359237 kg 1 mile = 1.609344 km 1 nautical mile = 1,852 m 1 US gallon = 3.785411784 L 1 UK gallon = 4.54609 L Temperature has an offset, not just a factor: °F = °C × 9/5 + 32 K = °C + 273.15
How it works
Almost every conversion is a single multiplication, because almost every unit is a fixed multiple of another. Since an international agreement in 1959, an inch has been exactly 2.54 centimetres and a pound exactly 0.45359237 kilograms; a foot, a yard, a mile, an acre, an ounce and a stone are all defined from those. So none of the figures here is an approximation to be rounded: a mile is 1.609344 kilometres to the last digit, and every result is exact until it is shown on screen.
Volume is where the names mislead. A US gallon and a UK gallon are different units — 3.785 litres against 4.546 — and so are the pints and fluid ounces built from them. A UK pint is 20 UK fluid ounces and a US pint is 16 US fluid ounces, which is why a pint of milk is about a sixth smaller in the United States. This converter keeps US and UK units separate and labelled, rather than offering a "gallon" and leaving you to guess which.
Weight has the same trap with the ton. A tonne is 1,000 kg. A US ton, the short ton, is 2,000 pounds — about 907 kg. A UK ton, the long ton, is 2,240 pounds — about 1,016 kg. They are close enough to be confused and far enough apart to matter.
Temperature is the exception to the multiplication rule, because its scales do not start at the same zero. 0 °C is the freezing point of water, not an absence of heat, so converting needs an offset as well as a factor, and doubling a temperature in Celsius does not double anything physical. Conversions go through kelvin, which does start at absolute zero, and nothing colder than that is accepted.
Worked example
A marathon, a pint of milk and a fever, converted exactly
- 42.195 km ÷ 1.609344 = 26.2187575 mi
- 1 UK pint = 20 × 4.54609 ÷ 160 L = 568.26125 ml
- 1 US pint = 16 × 3.785411784 ÷ 128 L = 473.176473 ml
- The US pint is 83.3% of the UK one.
- 38.5 °C × 9/5 + 32 = 101.3 °F
A marathon is 26.22 miles; a US pint is a sixth smaller than a UK pint
How to use it
- Choose what you are converting: length, weight, temperature, volume, area or speed.
- Enter the value, and pick the unit it is in and the unit you want.
- Read the result, with the exact relation between the two units under it. Swap units reverses the conversion.
- The list below shows the same value in every unit of that kind at once.
What this tool does not do
- Six kinds of unit: length, weight, temperature, volume, area and speed. Data sizes, energy, pressure and time are not included.
- Results are shown to ten significant figures. The arithmetic behind them uses the exact definitions.
- Cooking cups and spoons are the US customary ones. Metric cups of 250 ml and other national cups are different sizes and are not offered.
- Regional and traditional units, such as the bigha, guntha or tola, are not included, because their size varies from place to place.
- Lengths, weights, volumes and areas cannot be negative; speeds can, to allow for direction. Temperatures cannot go below absolute zero.
Frequently asked questions
How many centimetres are in an inch?
Exactly 2.54. It is a definition rather than a measurement: since 1959 the inch has been defined as 25.4 millimetres. A foot is exactly 30.48 cm and a mile exactly 1.609344 km for the same reason.
How many pounds are in a kilogram?
About 2.20462. The exact definition runs the other way — a pound is exactly 0.45359237 kg — so a kilogram is 1 ÷ 0.45359237 pounds, which does not end. 70 kg is 154.32 lb, or 11.02 stone.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32: 37 °C × 1.8 + 32 = 98.6 °F. To go back, subtract 32 and multiply by 5/9. The two scales meet at −40, where −40 °C and −40 °F are the same temperature.
Is a US gallon the same as a UK gallon?
No. A US gallon is 3.785411784 litres and a UK, or imperial, gallon is 4.54609 litres, so the UK gallon is about 20% larger. The difference carries through to pints and fluid ounces, which is why a recipe or fuel figure needs to say which it means.
What is the difference between a ton and a tonne?
A tonne, or metric ton, is 1,000 kg. A US short ton is 2,000 pounds, about 907.18 kg, and a UK long ton is 2,240 pounds, about 1,016.05 kg. All three are listed separately here.
How many millilitres are in a cup?
A US cup is 236.5882365 ml, exactly half a US pint. Many recipes outside the US use a metric cup of 250 ml instead, which this converter does not list, so check which cup a recipe means before converting.
How do I convert km/h to mph?
Divide by 1.609344, the number of kilometres in a mile. 100 km/h is 62.14 mph, and 60 mph is 96.56 km/h.
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Last updated 13 September 2026.