How this calculator works
A percent is a number out of 100, so P% means P ÷ 100. Every percentage question is the same relationship — Part = Percent ÷ 100 × Whole — rearranged to find the missing piece.
What is P% of X? Part = P ÷ 100 × X
X is what % of Y? P = X ÷ Y × 100
X is P% of what? Whole = X ÷ (P ÷ 100)
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Question | What is P% of X? |
| Percent (P) | 15 % |
| Number (X) | 80 |
| Result | Value |
|---|---|
| Answer | 12 |
| 80 plus 15% | 92 |
| 80 minus 15% | 68 |
Step by step:
- 15% = 15 ÷ 100 = 0.15
- 0.15 × 80 = 12
Quick percentage table
Common percentages of 80.
| Percent of 80 | Answer |
|---|---|
| 5% | 4 |
| 10% | 8 |
| 12.5% | 10 |
| 15% | 12 |
| 20% | 16 |
| 25% | 20 |
| 30% | 24 |
| 33.33% | 26.664 |
| 50% | 40 |
| 75% | 60 |
Common mistakes to avoid
- Dividing by the wrong number — the “of” number is always the whole.
- Forgetting to move the decimal: 7% is 0.07, not 0.7.
Frequently asked questions
What is 15% of 80?
0.15 × 80 = 12.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100: 80 ÷ 200 × 100 = 40%.
How do I find the original number from a percentage?
Divide the part by the percent as a decimal: if 30 is 20% of a number, the number is 30 ÷ 0.20 = 150.