What is a unit converter?
A unit converter changes a measurement from one unit to another, such as kilometres to miles, kilograms to pounds or Celsius to Fahrenheit. Different countries use different systems, so conversions come up in cooking, travel, shopping, school work, engineering and sport.
This converter covers five categories: length, weight, volume, speed and temperature. It uses exact standard factors and updates the answer as you type. It works on phones, tablets and computers.
Exact factors and the temperature exception
Conversions are based on internationally defined values: 1 inch is exactly 2.54 centimetres, 1 mile is 1.609344 kilometres and 1 pound is 0.45359237 kilograms. So 10 miles is about 16.09 kilometres and 5 kilograms is about 11.02 pounds.
Temperature is different because the scales have different zero points. Fahrenheit equals Celsius multiplied by 9/5 plus 32, so 100 degrees Celsius is 212 degrees Fahrenheit. Kelvin equals Celsius plus 273.15. This tool handles those formulas for you.
Why conversions matter
Small conversion mistakes can cause real problems. A recipe that mixes cups and grams can fail, and a wrongly converted measurement can ruin a craft or building project. Students meet unit conversions in every science subject, and travellers meet them in road signs, weather forecasts and airline baggage limits. A converter with exact factors helps you avoid rounding errors, and checking that the answer looks sensible, for example that a mile is longer than a kilometre, catches most typing mistakes.
How to use it
- Choose a category, for example Length.
- Type the value you want to convert.
- Pick the unit to convert from and the unit to convert to.
- Read the result instantly, or use the swap button to reverse the direction.
Practical tips
- Cooking from a foreign recipe? Convert cups, ounces and millilitres before you start.
- For travel, convert speed limits between km/h and mph.
- The US gallon used here is about 3.785 litres and differs from the UK gallon.
- Round sensibly. Three or four decimals is plenty for everyday use.
Frequently asked questions
How accurate are the conversions?
They use standard defined factors, so the results are exact to the digits shown.
Are US and UK gallons the same?
No. This tool uses the US gallon.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32.
Can I convert negative numbers?
Yes, which is useful for temperatures below zero.
Is my input stored?
No. Everything runs in your browser.