Metric and imperial conversions without the clutter
Twelve converters and a set of dedicated pages for the conversions people actually look up. Exact definitional factors, unit tested, and no sign-up.
Live converter
Pick a category, type a value, and the result updates as you type.
All tools
Each tool page carries the formula, a reference table and answers to the questions people ask about those units.
Convert length, weight, temperature, area and speed
Convert litres, gallons, pints, cubic metres and fluid ounces
Convert seconds, minutes, hours, days, weeks and years
Convert bar, psi, pascal, atmospheres and mmHg
Convert degrees, radians, gradians, arcminutes and turns
Convert watts, kilowatts, horsepower and BTU per hour
Convert joules, kilowatt hours, calories and BTU
Calculate home electricity consumption and running costs
Convert cups, tablespoons, grams and millilitres
Convert height and weight, and calculate BMI
Convert MPG, L/100km and km/L
Convert bytes, kilobytes, megabytes, gigabytes and terabytes
Search terms
Dedicated pages, each with the conversion factor, a worked example and a quick-reference table.
Why this site
A foot is exactly 0.3048 m and a pound exactly 0.45359237 kg. This site uses the definitions, not rounded approximations, and a test suite holds them to ten decimal places.
Every page shows the formula and a worked example, so you can check the arithmetic rather than trusting a black box.
Gallons, pints and fluid ounces differ between the US and UK. They are listed separately everywhere, so you never have to guess which one is meant.
How it works
Almost every conversion here works the same way: the value is converted into a base unit, then out again into the target. Length runs through metres, mass through kilograms, volume through litres. Each unit needs only one number defining it, and any pair converts without a separate rule per combination.
Temperature is the exception. Celsius and Fahrenheit have different zero points as well as different degree sizes, so it needs an offset as well as a ratio. That is why Celsius to Fahrenheit is °C × 9/5 + 32 and not a single multiplication — the most common mistake in hand conversions.