How to Find a Percent of a Number

"Percent" means "per hundred", so 15% means 15 out of every 100, or 0.15. Finding a percent of a number means multiplying the number by that decimal.

Try it with your own problem ↓

The steps

Change the percent to a decimal by dividing by 100, which moves the decimal point two places to the left: 15% = 0.15.
Multiply the decimal by the number. The word "of" means multiply.
Check that it is reasonable: 50% is half, 10% is one-tenth, and 100% is the whole thing.

A worked example

What is 15% of 80?

Change 15% to a decimal: 15 ÷ 100 = 0.15.
Multiply: 0.15 × 80 = 12.
A mental-math way to check: 10% of 80 is 8, and 5% is half of that, 4. Then 8 + 4 = 12.

15% of 80 = 12.

Why it works

The word percent means "per hundred", so 15% of 80 is 15/100 of 80. Dividing 15 by 100 gives 0.15, and multiplying by 0.15 takes 15 hundredths of 80. It is the same calculation written two ways.

Try it with your own problem

Open the free The Hundred Grid with this example already filled in. It shows every step, and you can type over it with your own numbers.

Work it out: 15% of 80Opens The Hundred Grid with this example

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Common mistakes

Moving the decimal point the wrong way. 15% is 0.15, not 1.5 or 15.
Mistaking 5% for 0.5. A one-digit percent has a zero in front: 5% is 0.05.
Dividing instead of multiplying. "Of" means times.
Mixing up the part and the whole. "18 is what percent of 72" is 18 ÷ 72, not 72 ÷ 18.

Questions people ask

How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. For "18 is what percent of 72": 18 ÷ 72 = 0.25, which is 25%.

Can a percent be more than 100?

Yes. 150% of 24 is 1.5 × 24 = 36. It means more than the whole.

How do I find 10%, 5% or 1% quickly?

10% is one place left (8 for 80). 5% is half of 10%. 1% is two places left (0.8 for 80).

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