Skip to main content
Math formula

How to calculate percentage of a number

A percentage of a number finds a fraction of the whole using a percent scale.

See the formulaOpen calculator
Direct answer
Formula
result = percent / 100 * number

Use the table below to match each symbol with the right input. Keep units consistent before you start.

Percentage of a number formula
Start here when you only need the equation and variable names.
Formula
result = percent / 100 * number

A percentage of a number finds a fraction of the whole using a percent scale.

Variable meanings
Check each symbol, meaning, and unit before you calculate.
SymbolNameDescriptionUnit
percentPercentThe percent rate.percent
numberNumberThe whole amount.Depends on inputs
resultResultThe portion of the number.Depends on inputs
When to use this formula
Check that your situation matches the formula before you trust the result.
  • Works for discounts, tips, taxes, grades, and other percent-of-whole questions.
Step-by-step method
Follow these steps when you are solving it by hand.
  1. 1Convert the percent to a decimal.
  2. 2Multiply by the number.
  3. 3Keep the same unit as the original number.
Examples
These sample numbers show the order of operations and units.
Find 15% of 80
percent
15
number
80
  1. 1.result = 15 / 100 * 80
  2. 2.result = 0.15 * 80
  3. 3.result = 12
Result
15% of 80 is 12.
Find 7.5% of 240
percent
7.5
number
240
  1. 1.result = 7.5 / 100 * 240
  2. 2.result = 0.075 * 240
  3. 3.result = 18
Result
7.5% of 240 is 18.
Mistakes to avoid
Small input or unit errors can change the answer a lot.
  • Putting the wrong value in the numerator or denominator of the percentage of a number formula.
  • Skipping signs, order, or sorting rules that change the result.
  • Rounding before the last step.
  • Assuming a formula applies when the needed input is zero or missing.
Open the Percentage Calculator
Open the calculator for the answer without rewriting the formula.

Enter your values in the related calculator, then compare the output with the hand method above.

Open Percentage Calculator
FAQs
Short answers for common formula questions.
Can I calculate Percentage of a number by hand?

Yes. Write the units next to each value, convert rates or measurements first, and round only the final answer.

Why does my Percentage of a number result differ from another calculator?

Most differences come from rounding, unit conversions, rate timing, or a slightly different version of the formula.

When is the Percentage Calculator better than hand math?

Open the Percentage Calculator to check several scenarios or skip the hand arithmetic.