Converters
Weight, length, temperature, number bases, fractions and colour codes, converted with exact factors.
All Converters
Weight Converter
Convert between kilograms, pounds, grams, ounces and stone, with the exact conversion factors shown.
Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin and Rankine, with landmark temperatures shown in whichever scale you picked.
Length Converter
Convert nine length units, from millimetres to nautical miles, with every customary factor derived from the exactly defined inch.
Decimal to Fraction / Fraction to Decimal
Turn a decimal into its closest simple fraction and its exact fraction, or turn a fraction back into a repeating decimal.
Number Base Converter
Convert whole numbers between any bases from 2 to 36, computed with BigInt so long hexadecimal values keep every digit.
Colour Code Converter
Convert a colour between HEX, RGB, HSL and CMYK, with a live swatch and WCAG contrast ratios against white and black text.
What to know about converters
Most unit conversions people need are exact by definition. An inch is exactly 2.54 cm, a pound is exactly 0.45359237 kg, and a mile is exactly 1609.344 m. Those are definitions agreed in 1959, not measurements. These tools compute from the defined values instead of a rounded constant, so you actually get the precision you ask for.
Temperature is the exception that catches people out. Celsius and Fahrenheit have different zero points as well as different step sizes, so you can't convert a temperature difference the same way you convert a temperature.
The number and colour converters also refuse to guess. Give the base converter a digit that doesn't exist in the base you chose and it tells you, instead of quietly dropping the character and returning a confident wrong answer.
Frequently asked
How many decimal places should I use?
More decimal places than your measurement justifies is false precision. If you measured to the nearest centimetre, ten decimal places of inches tells you nothing real. They're there for cases where the conversion feeds another calculation.
Why does converting back not give exactly my original number?
Rounding at each step. Convert 1 kg to pounds, round the display, then convert that rounded figure back and you land slightly off. Convert in one step from the original where you can.
Can I convert a temperature difference?
Not with this tool. A 10 °C rise is an 18 °F rise, not 50 °F, because the offset only applies to absolute temperatures and not to intervals.