Unit Converter with Exact Formulas
Convert values between units in ten categories using exact, internationally defined factors. Every conversion shows its formula and a table of the value in every other unit in the category.
How to convert units
- Choose a category such as Length or Temperature.
- Type the value and pick the units to convert from and to. Use the swap button to reverse them.
- Read the result and its conversion formula.
- Check the table below for the same value in every unit of the category.
Why temperature is different
Most units convert by a single multiplication, but Celsius and Fahrenheit have different zero points, so they need an offset as well: °F = °C × 9/5 + 32. The converter applies these formulas exactly and won't accept values below absolute zero. For file sizes and transfer times specifically, the File Size Converter goes into more detail on decimal and binary units.
Benefits
- Uses exact definitions, such as 1 inch = 2.54 cm and 1 pound = 0.45359237 kg, rather than rounded approximations.
- Keeps US and imperial gallons, pints and fluid ounces apart.
- The all-units table answers several conversions at once.
Limitations
- Results are shown to 12 significant digits. Floating-point arithmetic limits precision to about 15 digits.
- Month and year use average Gregorian lengths. Calendar-aware durations belong in the date difference calculator.
Privacy and security
Every number you type is calculated by JavaScript in this browser tab. Nothing is sent to a server or saved after you close the page.
Read our privacy policy for details about the site as a whole.
Frequently asked questions
How many kilometres are in a mile?
Exactly 1.609344 km. The international mile is defined as 1,760 yards, and the yard as exactly 0.9144 m.
What's the difference between GB and GiB?
A gigabyte (GB) is 1,000,000,000 bytes and a gibibyte (GiB) is 1,073,741,824 bytes. Drive makers use GB, while many operating systems report GiB but label it GB.
Is a US gallon the same as a UK gallon?
No. A US gallon is 3.785411784 litres and an imperial (UK) gallon is 4.54609 litres, about 20% larger. Pints and fluid ounces differ in the same way.