About this calculator
Percentage questions show up everywhere — grading a test, calculating a raise, figuring out a markup — and the three common versions of the question (what is X% of Y, what percent is X of Y, and what number is Y% of X) are each solved slightly differently. This calculator handles the most common version directly: finding what a given percentage of a number equals.
How it works
The calculation is X × (percent / 100). For example, 20% of 150 is calculated as 150 × (20/100) = 30. The same underlying formula rearranges to answer the other two common percentage questions: to find what percent X is of Y, calculate (X / Y) × 100; to find the original number when you know a percentage of it, divide the known amount by the percentage expressed as a decimal.
Worked example
20% of 150 is 30, calculated as 150 × (20 / 100). Reversed: 30 is what percent of 150? (30 / 150) × 100 = 20%.
Frequently asked questions
How do I find what percent one number is of another?
Divide the first number by the second, then multiply by 100. For example, to find what percent 30 is of 150: (30 / 150) × 100 = 20%.
How do I work backward from a percentage to the original number?
Divide the known amount by the percentage as a decimal. If $30 is 20% of an unknown amount, calculate 30 / 0.20 = $150.
How is percentage change different from a straight percentage?
Percentage change compares an old and new value: (new − old) / old × 100. That's a different question from 'what is X% of Y,' so make sure you're using the right formula for what you're actually trying to find.
Last reviewed: September 2026.