Conversion Calculator
Pick a category, the unit you have and the unit you want, enter the value and press Convert. The calculator covers nine categories: length, weight, volume, area, speed, temperature, energy, pressure and time. The volume units are US measures, so a gallon is the US gallon and a cup is the US cup. The result shows up to 8 decimal places, worked out from the exact definition of each unit.
How to use the Conversion Calculator
- Enter your numbers in the Conversion Calculator above.
- Press the Convert button to see the result.
- To try other numbers, change any value and press the button again.
The unit conversion principle
Target value = Source value × (size of the source unit ÷ size of the target unit) · · · °F = °C × 9/5 + 32 · · · K = °C + 273.15
Each unit has a fixed size in a base unit. A yard is 0.9144 meters and a pound is 0.45359237 kilograms, the definitions in the UK Weights and Measures Act 1985. A calorie is 4.184 joules, a BTU is 1,055.05585262 joules and a standard atmosphere is 101,325 pascals, as NIST lists them. A year here is the average Gregorian year of 365.2425 days, and a month is 1/12 of that. Temperature needs an offset as well as a factor, because Celsius and Fahrenheit start from different zero points. The calculator turns down temperatures below absolute zero, 0 K.
Worked example
100 km/h is 62.13711922 mph. 70 kg is 154.32358353 lb. 25 °C is 77 °F. 1 US gallon is 3.78541178 liters. 1 kilowatt-hour is 3,412.14163313 BTU. 1 atmosphere is 14.69594878 psi. 90 minutes is 1.5 hours.
Frequently asked questions
Are US and UK gallons different?
Yes. NIST lists the US gallon as 3.785 412 liters, rounded to 7 digits. The UK (imperial) gallon is 4.54609 liters, as the UK Weights and Measures Act 1985 defines it. This calculator uses the US gallon, and US quarts, pints, cups and fluid ounces. To get liters from imperial gallons, multiply by 4.54609.
How precise are the results?
The calculator works from the exact size of each unit and the value as you type it, and rounds once, to 8 decimal places. It drops trailing zeros, so 1 foot shows 12 inches and 1 inch shows 2.54 centimeters.
Which calorie and BTU does it use?
The thermochemical calorie of 4.184 joules and the International Table BTU of 1,055.05585262 joules, both from NIST. A food Calorie on a label is a kilocalorie, so pick Food Calories (kcal) for those. Other BTU definitions differ by a small amount, and this page does not offer them.
Are mmHg and torr the same?
Almost. A torr is exactly 1/760 of a standard atmosphere, 133.32236842 pascals. A conventional millimeter of mercury is 133.32238742 pascals. They first differ in the eighth digit, and NIST prints both as 133.3224. The inHg here is 25.4 conventional mmHg.
How long are a month and a year here?
They are averages. A year is 365.2425 days, the average Gregorian year, and a month is 1/12 of that, 30.436875 days. So 1 year is 12 months and 1 month is 4.348125 weeks. For the time between two dates, use the date calculator.
Why do temperature units have offsets?
Celsius and Fahrenheit have different zero points. Kelvin is an absolute scale (zero = absolute zero) and converts to Celsius by simple offset: K = °C + 273.15.