How to Calculate the Percentage of a Number

Whether you're figuring out a tip at a restaurant, calculating a discount while shopping, or working through a school assignment, knowing how to find a percentage of a number is one of the most useful math skills you can have. This guide walks you through it clearly and simply.

The Core Formula

The fundamental formula for finding a percentage of a number is:

Result = (Percentage ÷ 100) × Total Number

That's it. Once you understand this formula, you can solve almost any percentage problem.

Step-by-Step Example

Let's say you want to find 30% of 150.

  1. Write down your percentage: 30%
  2. Divide it by 100: 30 ÷ 100 = 0.30
  3. Multiply by the total number: 0.30 × 150 = 45

So, 30% of 150 is 45.

More Worked Examples

Problem Step 1 (÷100) Step 2 (×Number) Answer
15% of 200 0.15 0.15 × 200 30
25% of 80 0.25 0.25 × 80 20
8% of 500 0.08 0.08 × 500 40
60% of 45 0.60 0.60 × 45 27

How to Find What Percentage One Number Is of Another

Sometimes the question is flipped — you want to know: "What percentage is 45 of 150?"

Use this formula:

Percentage = (Part ÷ Whole) × 100

  1. Divide the part by the whole: 45 ÷ 150 = 0.30
  2. Multiply by 100: 0.30 × 100 = 30

So 45 is 30% of 150 — the reverse of our first example.

Finding the Original Number from a Percentage

Another common problem: "30% of what number is 45?"

Whole = Part ÷ (Percentage ÷ 100)

  1. Divide the percentage by 100: 30 ÷ 100 = 0.30
  2. Divide the part by that decimal: 45 ÷ 0.30 = 150

The original number is 150.

Quick Tips to Remember

  • Percent means "per hundred" — so 40% literally means 40 out of every 100.
  • Dividing by 100 converts a percentage to a decimal you can multiply with.
  • When in doubt, use the triangle: Part = Whole × Rate, rearranged for whichever piece you're missing.
  • Use a calculator for accuracy when numbers get complex.

Summary

The three core percentage calculations are:

  • Find the part: Part = (% ÷ 100) × Whole
  • Find the percentage: % = (Part ÷ Whole) × 100
  • Find the whole: Whole = Part ÷ (% ÷ 100)

With these three formulas in hand, you can tackle virtually any percentage problem you encounter in daily life.