How to Calculate Percentages
Learn the basic percentage formula, how to find a percentage of a number, and how to find the original whole when you know a part and a percentage.
Quick answer
To find what percentage one number is of another, divide the part by the whole and multiply by 100.
Percentage = (Part ÷ Whole) × 100What is a percentage?
A percentage is a way of expressing a number as a part of 100. The word “percent” means “per hundred,” so 25% means 25 out of every 100.
Percentages make it easier to compare parts of different-sized totals. For example, 20 correct answers out of 25 and 80 correct answers out of 100 both equal 80%.
The basic percentage formula
Use the basic formula when you know the part and the whole and want to find the percentage.
The part is the amount you are comparing. The whole is the complete total. Divide the part by the whole first, then multiply by 100 and add the percent symbol.
Example: What percentage is 18 out of 24?
- Divide the part by the whole: 18 ÷ 24 = 0.75
- Multiply by 100: 0.75 × 100 = 75
- Add the percent sign: 75%
Answer: 18 is 75% of 24.
Find what percentage one number is of another
Questions such as “What percent is 12 of 48?” use the part-over-whole formula. Place the amount named after “is” over the amount named after “of.”
Example: What percent is 12 of 48?
- Divide 12 by 48: 12 ÷ 48 = 0.25
- Multiply by 100: 0.25 × 100 = 25
Answer: 12 is 25% of 48.
Example: You answered 37 questions correctly out of 40
- Divide 37 by 40: 37 ÷ 40 = 0.925
- Multiply by 100: 0.925 × 100 = 92.5
Answer: Your score is 92.5%.
Find a percentage of a number
To find a known percentage of an amount, convert the percentage to a decimal and multiply by the whole number. Divide the percentage by 100 to convert it to a decimal.
Example: What is 15% of 80?
- Convert 15% to a decimal: 15 ÷ 100 = 0.15
- Multiply by 80: 80 × 0.15 = 12
Answer: 15% of 80 is 12.
Example: What is 8% of $250?
- Convert 8% to a decimal: 0.08
- Multiply by $250: $250 × 0.08 = $20
Answer: 8% of $250 is $20.
Find the whole from a percentage
Sometimes you know a part and the percentage it represents, but not the original total. Convert the percentage to a decimal, then divide the known part by that decimal.
Example: 30 is 15% of what number?
- Convert 15% to a decimal: 0.15
- Divide the part by the decimal: 30 ÷ 0.15 = 200
Answer: 30 is 15% of 200.
Example: A $45 discount is 30% of the original price
- Convert 30% to a decimal: 0.30
- Divide $45 by 0.30: $45 ÷ 0.30 = $150
Answer: The original price was $150.
Common percentage mistakes
Using the wrong whole
The whole is the original total being measured. If 18 people out of 24 selected an option, use 24 as the denominator, not 18.
Forgetting to multiply by 100
Dividing 18 by 24 gives 0.75. That is the decimal form. Multiply by 100 to express it as 75%.
Mixing up “percent of” and “percent increase”
“What is 15% of 80?” uses multiplication. A percentage increase or decrease compares a change with the starting value. See the percent increase guide for that calculation.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 to convert it to a decimal, then multiply by the number. For example, 25% of 60 is 0.25 × 60 = 15.
How do I find what percentage one number is of another?
Divide the first number by the second number and multiply by 100. For example, 12 ÷ 48 × 100 = 25%, so 12 is 25% of 48.
How do I calculate 20% of an amount?
Multiply the amount by 0.20. For example, 20% of $150 is $150 × 0.20 = $30.
How do I find the original number from a percentage?
Divide the known part by the percentage written as a decimal. If $30 is 15% of a total, calculate $30 ÷ 0.15 = $200.
What does percent mean?
Percent means “per hundred.” For example, 7% means 7 for every 100, which is also written as the decimal 0.07.