How to calculate a percentage
A percent is a number out of 100, so every percentage question uses the same relationship between the part, the percent and the whole.
Here it is with your numbers:
- Turn the percent into a decimal: 15 ÷ 100 = 0.15.
- Multiply by the whole: 0.15 × 80 = 12.
It means 15% of 80 is 12, and the other 85% is 68.
Source Khan Academy · Percentages lesson ↗
Common percentages of 80
| Percent | As a decimal | Of your number |
|---|---|---|
| 5%You | 0.05 | 4 |
| 10%You | 0.1 | 8 |
| 15%You | 0.15 | 12 |
| 20%You | 0.2 | 16 |
| 25%You | 0.25 | 20 |
| 50%You | 0.5 | 40 |
| 75%You | 0.75 | 60 |
| 100%You | 1 | 80 |
Use it in Excel or Google Sheets
Type these into any cell. Spreadsheets understand the % sign, so you don't need to divide by 100 yourself.
| To find | Example |
|---|---|
| A percent of a number | =800*8.9% → 71.2 |
| What percent a part is | =42/50 → 84% |
| The whole from a part | =15/75% → 20 |
To show the answer as a percent, format the cell as Percentage.
Source Microsoft Support · Calculate percentages ↗
FAQs
How do I calculate a percentage?
Divide the part by the whole, then multiply by 100. For example, 42 out of 50 is 42 ÷ 50 = 0.84, which is 84%.
How do I find a percentage of a number?
Turn the percent into a decimal by dividing by 100, then multiply. For example, 30% of 6 is 0.30 × 6 = 1.8.
How do I find the whole when I know a part and its percent?
Divide the part by the percent as a decimal. If $15 is 75% of the original price, the original was 15 ÷ 0.75 = $20.
How do I turn a percentage into a decimal?
Remove the % sign and move the decimal point two places to the left. 15% becomes 0.15, and 8.9% becomes 0.089.