What a percentage means
Percent means “per hundred.” A percentage describes a part relative to a whole using 100 as the common scale. The expressions 35%, 35/100 and 0.35 all represent the same proportion.
Find a percentage of a number
When the percentage and the number are known, convert the percentage to a decimal and multiply. The equivalent one-line formula is:
Result = Percentage × Number ÷ 100
Example: What is 18% of 250?
- Multiply 18 by 250 to get 4,500.
- Divide 4,500 by 100 to get 45.
18% of 250 is 45.
Find what percent one value is of another
Treat the value being measured as the part and the reference amount as the total. Divide the part by the total, then multiply by 100.
Percentage = Value ÷ Total × 100
Example: 24 is what percent of 80?
24 ÷ 80 × 100 = 30%
24 is 30% of 80.
Find the whole from a part and a percentage
For a reverse percentage question, divide the known part by the percentage written as a decimal.
Whole = Part ÷ (Percentage ÷ 100)
If 30 is 15% of an unknown whole, then 30 ÷ 0.15 = 200.
Choose the correct baseline
The denominator controls the meaning of the answer. For a test score, the total number of questions is the baseline. For percentage increase, the original value is the baseline. Label the part, total and original value before calculating to avoid reversing them.
Common percentage mistakes
- Swapping the part and the whole.
- Using 20 instead of 0.20 when multiplying directly.
- Rounding intermediate steps too early.
- Calling a five percentage-point rise a 5% increase.
Related calculators
Use a focused tool to check the method with your own values.