How to find a percentage of a number
To find X% of a number, convert the percent to a decimal and multiply: result = number × (percent ÷ 100). For 20% of 150: 150 × 0.20 = 30. "Per cent" literally means "per hundred," so 20% is 20 per 100.
Because multiplication commutes, X% of Y always equals Y% of X. That is a genuinely useful shortcut: 18% of 50 is awkward, but 50% of 18 is obviously 9. A percent is just a fraction with 100 on the bottom, so the fraction to decimal calculator produces the same multiplier.
How to use this calculator
Enter the percent and the number. The result is that share of the number. For a change rather than a share, see the percentage increase and percentage change calculators.
Enter the percent as a plain number — type 20, not 0.20, or the answer will be a hundred times too small. The result carries whatever unit the number had, so 20% of 150 dollars is 30 dollars.
Percentages in everyday use
Tips, tax, discounts and interest are all the same calculation. A 20% tip on a 150 bill is 30; a 20% discount takes 30 off, leaving 120. Note the difference between finding a share and applying a change — a discount needs the subtraction step afterwards.
One frequent mistake is chaining percentages by adding them. A 20% discount followed by a further 10% is not 30% off: the second cut applies to the already-reduced figure, so 150 becomes 120 and then 108, an effective 28% reduction.
Frequently asked questions
- How do I calculate a percentage of a number?
- Multiply the number by the percent divided by 100. 20% of 150 is 150 × 0.20 = 30.
- What is 20% of 150?
- 30.
- How do I turn a percent into a decimal?
- Divide it by 100. 20% becomes 0.20.
- How do I find what percent one number is of another?
- Divide the part by the whole and multiply by 100. 30 out of 150 is 30 ÷ 150 × 100 = 20%.
- Can I enter a percentage over 100 or a negative one?
- Yes. A percent above 100 simply returns more than the original number — 150% of 150 is 225. A negative percent returns a negative result, which is useful for representing a reduction or a loss against a base figure.