To find the percentage of a number, convert the percentage to a decimal and multiply. The formula is: result = (percentage ÷ 100) × number. This is the everyday "what is X% of Y?" question, and it is the single most common percentage calculation people need.
The two-step method
- Divide the percentage by 100 to turn it into a decimal. For 30%, that is 0.30.
- Multiply that decimal by the number you are taking the percentage of.
Example: what is 30% of 250? First, 30 ÷ 100 = 0.30. Then 0.30 × 250 = 75. So 30% of 250 is 75.
More worked examples
- 15% of 80 = 0.15 × 80 = 12
- 7.5% of 400 = 0.075 × 400 = 30
- 125% of 40 = 1.25 × 40 = 50 (percentages above 100 give a result larger than the original)
- 0.5% of 2,000 = 0.005 × 2,000 = 10
A quick mental shortcut
Because multiplication is commutative, X% of Y equals Y% of X. So 8% of 50 is the same as 50% of 8, which is 4. Swapping the numbers often turns an awkward calculation into an easy one, especially with percentages like 25, 50 or 10.
Percentage of a number at a glance
| Question | Decimal form | Result |
|---|---|---|
| 10% of 90 | 0.10 × 90 | 9 |
| 20% of 150 | 0.20 × 150 | 30 |
| 33% of 300 | 0.33 × 300 | 99 |
| 75% of 64 | 0.75 × 64 | 48 |
Common uses
You use "X% of Y" constantly: a 20% tip on a bill, a 15% tax added at checkout, a 40% discount on a price, interest earned on savings, or a commission on a sale. Each one is the same multiply-by-decimal step.
Watch for the base
The trickiest part is knowing which number is the base. When a store says "20% off", the base is the original full price, not the sale price. When you calculate a tip, the base is usually the pre-tax bill. Always identify Y before multiplying, or you will apply the percentage to the wrong amount.
Percentage of a number vs percent change
Do not confuse "the percentage of a number" with a percent change. Finding 25% of 200 gives a fixed amount (50). A percent change asks how much a value moved relative to where it started. In the first case the percentage acts like a share of a total; in the second it describes movement. The formulas look similar, so read the question carefully: "what is 25% of 200" is multiplication, while "200 increased by 25%" starts from the same 50 but adds it to the base.
Enter the percentage and the number in Mode 1 of our percentage calculator to get the answer instantly, and see how to calculate a discount percentage when the base is a sale price.