How to convert units
- Pick a category such as Length, Weight or Temperature.
- Type a value and choose the unit you’re starting from.
- Read the result, or look at the table that lists the value in every unit. Click a number to copy it.
How it works
Each unit is stored as an exact factor to the SI base unit, taken from official definitions: an inch is exactly 2.54 cm, a pound exactly 0.45359237 kg, a US gallon exactly 3.785411784 L. Temperature uses formulas instead of factors, because 0 °C is not 0 °F.
Results are rounded to 12 significant digits, enough for engineering work without floating-point noise like 2.5399999999.
Worked examples
- 1 inch = 2.54 cm, so a 27-inch monitor has a diagonal of 68.58 cm.
- 100 km/h = 62.14 mph.
- 37 °C = 98.6 °F; 0 °C = 32 °F.
- A drive sold as 1 TB holds 1,000,000,000,000 bytes, which is 931.32 GiB. That’s why your computer shows less than the box says.
- 1 kcal = 4.184 kJ, so a 250 kcal snack is 1,046 kJ.
When to use it
Reading a recipe in cups, a tire pressure in psi, a weather forecast in °F or a body weight in pounds. Comparing apartment sizes in square feet and square meters. Understanding why a 512 GB phone shows about 477 GB.
For percentages and price changes, use Percentage Calculator. For date differences and deadlines, use Date, Age & D-day Calculator.
Limits
- Month and year are averages; for exact calendar math use the date calculator.
- Cooking cups vary by country (the US cup is 236.6 mL; many recipes elsewhere use 200 or 250 mL).
- Commas and dots are both accepted as decimal marks, but write large numbers without thousand separators to be safe.
Frequently asked questions
How many centimeters is an inch?
Exactly 2.54 cm. The inch has been defined that way since 1959.
How do I convert °C to °F?
Multiply by 9/5 and add 32. For example, 20 °C × 1.8 + 32 = 68 °F.
Why does my 1 TB drive show 931 GB?
Manufacturers count 1 TB as 10^12 bytes; many operating systems divide by 1024 three times and call the result GB. Both are the same number of bytes.
Does it work offline?
Yes. Once the page has loaded, all conversions run in your browser.