Which tool should you use?
- Changing units, like inches to centimetres, pounds to kilograms or °F to °C: Unit Converter.
- Anything with “%”: a discount, a tip, a tax, what share one number is of another, or how much something went up or down: Percentage Calculator.
Typical workflows
Both tools show the formula next to the answer. That makes them useful for homework and for double-checking a spreadsheet, not just for getting a number. For date arithmetic, such as days between two dates or someone’s age, use Date, Age & D-day Calculator.
Frequently asked questions
How precise are the results?
Conversions use exact definitions where they exist (1 inch is exactly 2.54 cm, 1 pound is exactly 0.45359237 kg). Results are rounded only for display.
Why is a 20% rise followed by a 20% fall not back to the start?
Because the second 20% is taken from a bigger number. 100 → 120 → 96. The percentage calculator shows this step by step.