Converters Units
Length, weight, temperature, data and speed with exact factors.
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cm to inches
Convert centimetres to inches and back using the exact international factor, with a reference chart and the formula shown.
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kg to lbs
Convert kilograms to pounds and back with the exact international factor, plus a reference chart and stone conversions.
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Celsius to Fahrenheit
Convert °C to °F and back with the formula shown, plus a reference chart of everyday and body temperatures.
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Feet to metres
Convert feet to metres and back with the exact international factor, plus a chart covering heights, room sizes and altitudes.
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Miles to km
Convert miles to kilometres and back with the exact factor, plus speed limits, running distances and a reference chart.
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MB to GB
Convert megabytes to gigabytes in both the decimal (1000) and binary (1024) conventions, and see why your drive looks smaller than the box said.
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mph to km/h
Convert mph to km/h with the exact factor, plus a speed-limit chart for driving abroad and the mental arithmetic that gets you close.
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sq ft to sq m
Convert square feet to square metres with the exact factor, plus why area conversion squares the length factor and a chart of common property sizes.
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Gallons to litres
Convert US and imperial gallons to litres with exact factors, and see why the two gallons differ by twenty per cent.
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Inches to cm
Convert inches to centimetres with the exact factor of 2.54, plus screen sizes, paper sizes and a full reference chart.
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lbs to kg
Convert pounds to kilograms with the exact factor, plus body weight, luggage allowance and gym plate references.
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Fahrenheit to Celsius
Convert °F to °C with the formula shown, plus oven temperatures, body temperature and a weather reference chart.
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KB to MB
Convert kilobytes to megabytes in both the decimal and binary conventions, with a reference chart of common file sizes.
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Cups to ml
Convert cups to millilitres, with the three different cups explained and a note on why baking should be weighed instead.
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Knots to km/h
Convert knots to km/h and mph with the exact factor, plus a Beaufort wind scale reference and why aviation still uses them.
Exact factors, not rounded ones
Every metric-to-imperial factor on this site is the internationally agreed exact value from the 1959 International Yard and Pound Agreement: an inch is exactly 2.54 cm, a pound is exactly 0.45359237 kg, a mile is exactly 1,609.344 m. These are definitions, not measurements, and each converter shows the factor it used so you can check the arithmetic yourself.
Temperature works differently
Length and weight conversions are proportional: double the input, double the output. Temperature scales are affine. They have different zero points, so converting requires an offset as well as a ratio. That is why °C to °F needs the +32, and why you cannot convert a temperature difference the same way you convert a temperature.
Every page works in both directions
Each converter has two input boxes and swaps freely, so type in either one and the other follows. The unit selectors cover the whole dimension, so the centimetres-to-inches page will just as happily convert nautical miles to millimetres if that is what you need.
Reference tables
Each page carries a printed conversion chart alongside the calculator, because a good many people arriving at a converter want to scan a table rather than type a number. The tables are generated from the same exact factors, so they never drift from the calculator above them.
