Unit Converter

Unit Converter turns one measurement into another while you type: centimetres into inches, kilograms into stones and pounds, Celsius into Fahrenheit, cups of flour into grams, gigabytes into the “GB” Windows shows, miles per gallon into litres per 100 km. Type into either box and the other one updates.

Every factor comes from the official definition rather than a rounded table: an inch is exactly 2.54 cm, a pound exactly 0.45359237 kg, a US gallon exactly 3.785411784 litres. That is why 1 inch shows as exactly 2.54, not 2.5399999. Answers show ten significant figures unless you pick tidier rounding, such as two decimals or three significant figures.

US and UK pints, gallons, cups and fluid ounces are separate and clearly labelled. Decimal megabytes and binary mebibytes sit side by side with a plain explanation. Fuel economy is handled as the upside-down conversion it really is. Everything runs in your browser, so it keeps working offline once loaded.

1. Pick what you are converting, such as Length, Weight or Cooking, or tap one of the “Popular” shortcuts like “cm ↔ in”.
2. Type a number in the “From” box. Fractions such as 1/2 or 1½ work, and in Length or Weight you can type 5'11 or 11 st 4.
3. Choose the two units from the menus. Press the round swap button to turn the conversion around.
4. Read the answer in the “To” box, or type there instead to convert the other way. Set “Rounding” if you want fewer digits.
5. Press “Copy result”, or scroll to the table that shows your number in every unit and tap “Copy” next to the one you need.

• Sixteen kinds of unit: length, weight, temperature, volume, area, speed, time, cooking, data storage, data speed, fuel economy, pressure, energy, power, angle and frequency.
• Exact defined factors for inches, feet, miles, pounds, ounces, gallons, pints and pounds per square inch.
• Feet and inches and stones and pounds shown under length and weight results, and typed input such as 5'11 or 11 st 4 lb understood.
• US and UK cups, pints, quarts, gallons and fluid ounces kept apart, plus metric cups and Australian 20 mL tablespoons.
• Cups and spoons to grams for 13 common ingredients, from flour and sugar to butter, honey and rice.
• Decimal kB, MB, GB and TB next to binary KiB, MiB, GiB and TiB, and bits next to bytes for internet speeds.
• Fuel economy that converts mpg (US or UK) to litres per 100 km correctly, as an inverse, not a simple multiplier.
• A table of your number in every unit, with copy buttons, and a formula line such as “1 in = 2.54 cm”.
• Two-way, live conversion, rounding from whole numbers to 8 significant figures, and your last category and units remembered.

• Converting a temperature change, such as “the oven runs 10 °C hot”, is different from converting a temperature: a 10 °C difference is 18 °F, not 50 °F.
• Check which gallon a figure uses. A car rated 40 mpg in the UK is about 33 mpg in US terms, because the UK gallon is bigger.
• For baking, cups to grams is only a guide: how you fill the cup changes the weight. If a recipe gives grams, weigh instead.
• In either box, the arrow keys nudge the number by 1, and by 10 with Shift held.