Key takeaway
To find the percent of a number, convert the percent to a decimal (÷100) and multiply by the number. The three reliable steps are: write the percent as a decimal, multiply by the number, and keep the unit. Mental tricks (10% = shift one place) speed up common rates.
Scope and assumptions
General arithmetic. Some rates are tiered or compounded in real life. This site is informational and not official.
Short answer: To find the percent of a number, convert the percent to a decimal (÷100) and multiply by the number. The three reliable steps are: write the percent as a decimal, multiply by the number, and keep the unit. Mental tricks (10% = shift one place) speed up common rates. This page is the step-by-step method; for why the formula works as a fraction over 100, see Percentage of a Number.
Quick navigation
- X% of Y → x-percent-of-y
- % of a number → percentage-of-a-number
- % to decimal → percent-to-decimal
- The calculator → Percentage Calculator
1. Three steps
- Write the percent as a decimal — 15% → 0.15.
- Multiply by the number — 0.15 × 200 = 30.
- Keep the unit — 30 (dollars, marks, items).
That is the entire method for finding any percent of any number.
2. Practice set
| Percent | Number | Decimal × Number | Result |
|---|---|---|---|
| 15% | 200 | 0.15 × 200 | 30 |
| 40% | 75 | 0.40 × 75 | 30 |
| 12% | 150 | 0.12 × 150 | 18 |
| 33% | 300 | 0.33 × 300 | 99 |
3. Mental tricks
- 10% — shift decimal one place left (10% of 450 = 45).
- 1% — shift two places left (1% of 800 = 8).
- 5% — half of 10%.
- 20% — 10% × 2.
- Any % — find 1%, then multiply by the percent (e.g. 17% of 400 = 4 × 17 = 68).
4. When the number is a percent itself
Finding 25% of 60%:
0.25 × 0.60 = 0.15 = 15%
So 25% of 60% is 15 percentage points of the whole — see percent-vs-percentage-point for why that wording matters.
5. Common mistakes
- Skipping the decimal conversion — 15 × 200 = 3000, not 30.
- Dropping the unit — the result carries the same unit as the number.
- Rounding the decimal too early — keep 0.33 exact until the end.
- Using % on a percent without care — the answer is itself a share, not a percent-of-percent confusion.
6. Build any percent from 1% and 10%
Find 1% of the number (shift two places left), then multiply by the percent you want. For 17% of 400: 1% = 4, so 17% = 4 × 17 = 68. For 35% of 200: 1% = 2, so 35% = 2 × 35 = 70. This mental method needs no decimal conversion and is exact for whole percents — handy when a calculator is not in hand, and it doubles as a check on the decimal method.
7. The decimal is the working form
Finding the percent of a number only works once the percent becomes a decimal. The phrase "15% of 200" is really "0.15 times 200", and the multiplication is the whole job. Skipping the decimal step is the one error that turns a tidy 30 into a useless 3000. Keep a short mental table: 10% is one tenth, 1% is one hundredth, and any other percent is a multiple of those two anchors. With the anchors in place, most "percent of a number" questions answer themselves without a calculator, and the answer is always smaller than the number unless the percent exceeds 100.
8. Anchor, then scale
The 1% and 10% anchors turn any percent into a small multiplication. For 23% of 300, 1% is 3, so 23% is 3 × 23 = 69. The method is exact for whole percents and far quicker than reaching for a calculator, and it doubles as a check on the decimal method. Build the anchor habit and "percent of a number" becomes a two-step mental sum rather than a formula you have to recall, which is why it survives long after the classroom rules fade from memory.
FAQ
Q: How do I find the percent of a number? Turn the percent into a decimal (÷100) and multiply by the number. 15% of 200 = 0.15 × 200 = 30.
Q: What is a fast trick for 10%? Move the decimal one place left: 10% of 450 = 45.
Q: How do I find 1% of a number? Move the decimal two places left: 1% of 800 = 8. Build other percents from there.
Q: Why convert to decimal first? Because % means per hundred; skipping it makes the answer 100× too large.
Sources: Khan Academy percentage basics; Maths is Fun — Introduction to Percentages.
Disclaimer: General arithmetic. Some rates are tiered or compounded in real life. This site is informational and not official.
Sources and references
- Khan Academy percentage basicshttps://www.khanacademy.org/math/pre-algebra/x31947de81e3f6453:percentages
- Maths is Fun — Introduction to Percentageshttps://www.mathsisfun.com/percentage.html