About the unit conversion calculator
This unit converter changes values between metric, US customary and imperial units across length, weight, temperature, area, volume, speed and time. Pick a category, enter a value and choose the units to convert from and to.
Conversions use exact internationally agreed factors, such as 1 inch = 25.4 mm exactly, and show the result to up to 10 significant digits, together with a table of the same value in every other unit of that category.
Who should use the unit conversion calculator
- Travellers and online shoppers moving between metric and US or UK units.
- Cooks, DIY builders and students.
- Engineers and writers who need a quick, reliable factor.
How to use the unit conversion calculator: what each input means
- Category
- Length, weight/mass, temperature, area, volume, speed or time.
- Value
- The number to convert.
- From and to units
- Metric, US and UK units are listed together.
How the unit conversion calculator works: method and formula
Each unit is defined as a factor relative to a base unit of its category (metre, kilogram, square metre, litre and so on). To convert, the value is multiplied by the source factor and divided by the target factor, which avoids chains of rounded conversions.
Temperature is handled separately because Celsius, Fahrenheit and Kelvin have different zero points, not just different scales.
- Linear units
- result = value × (factor of source ÷ factor of target)
- Fahrenheit to Celsius
- °C = (°F − 32) × 5 ÷ 9
- Celsius to Kelvin
- K = °C + 273.15
How to read your unit conversion calculator result
Check the units on the result label, especially for gallons (US and UK differ), tons (short, long and metric) and miles (statute versus nautical). The converter lists each separately so the difference is explicit.
Very large or very small results switch to exponent notation (for example 1.5e-7) to avoid long strings of zeros.
Unit Conversion Calculator worked example
Convert 10 kilometres to miles, 100 °F to °C, and 1 UK gallon to litres.
- 10 km ÷ 1.609344 = 6.2137 miles.
- (100 − 32) × 5 ÷ 9 = 37.78 °C.
- 1 UK gallon = 4.54609 litres, while 1 US gallon = 3.785412 litres.
10 km is 6.2137 miles; 100 °F is 37.78 °C.
Practical uses of the unit conversion calculator
- Converting recipes and clothing sizes' measurements.
- Checking product dimensions on overseas websites.
- Moving between stone, pounds and kilograms.
Assumptions and limitations of this calculator
- Currency conversion is not included because rates change constantly.
- Displayed results are rounded for readability; the underlying calculation uses full precision.
- Some historic or regional units (for example old trade units) are not listed.