How do I calculate what percentage one number is of another?

The formula

Percentage = (part / whole) x 100. So 45 of 180 is 45 / 180 = 0.25, times 100 = 25 percent. The same idea works in reverse: to find 20 percent of 150, multiply 150 by 0.20 to get 30. And to find the whole when you know the part, divide the part by the percentage as a decimal: if 30 is 20 percent of something, the whole is 30 / 0.20 = 150.

Where this shows up every day

Test scores, sale prices, budgets, savings goals and progress bars all reduce to this one calculation. The arithmetic is simple but easy to flip around in your head, which is exactly why a calculator that lets you type the two numbers and see the answer instantly is worth bookmarking.

Step by step

1. Divide the part by the whole. Take the smaller quantity and divide it by the total, for example 45 / 180 = 0.25.
2. Multiply by 100. Move the decimal two places: 0.25 becomes 25 percent.
3. Or use the calculator. Type both numbers into the free percentage calculator and read the result instantly.