How to Calculate What Percent One Number Is of Another
Formula: Part / Whole x 100. This is the classic "X is what percent of Y?" question. Divide the part by the whole, multiply by 100, and you have your percentage. It shows up in test scores, budget breakdowns, sales figures, and anywhere a slice needs to be measured against a total.
The Formula
To express one number as a percentage of another:
Percentage = Part / Whole x 100
The "whole" is whatever you are measuring against. The "part" is the piece of it you care about. Divide, multiply by 100, and that is your percentage.
Step-by-Step Examples
Example 1: Test score
You scored 68 marks out of a possible 80.
68 / 80 x 100 = 85%.
Your score is 85%.
Example 2: Budget spent
A project had a budget of $12,000. You have spent $9,000.
9,000 / 12,000 x 100 = 75%.
You are 75% through your budget.
Example 3: Sales target
Your monthly sales target is 250 units. You have sold 190.
190 / 250 x 100 = 76%.
You have reached 76% of your target.
Example 4: Nutrition label
A cereal bar contains 18 g of sugar. Your daily recommended intake is 90 g.
18 / 90 x 100 = 20%.
One bar uses 20% of your daily sugar allowance.
Example 5: Job applicants
You received 320 applications and shortlisted 48 candidates.
48 / 320 x 100 = 15%.
15% of applicants made the shortlist.
How to Identify the Part and the Whole
The question usually signals which is which:
- "18 is what percent OF 90?" The word "of" signals that 90 is the whole.
- "What percent of 200 is 50?" Again, 200 follows "of" and is the whole.
- "What fraction of the class passed?" The class size is the whole; the number who passed is the part.
When in doubt, ask: "Out of what total am I measuring?" That total is the whole.
When the Answer Exceeds 100%
If the part is larger than the whole, the answer tops 100%, which is perfectly valid. A company that earns $120,000 against a target of $80,000 has hit 150% of its target. 120,000 / 80,000 x 100 = 150%. Nothing breaks; the math just reflects that you exceeded the reference value.
Quick Conversion Table
| Part | Whole | Calculation | Percentage |
|---|---|---|---|
| 25 | 100 | 25 / 100 x 100 | 25% |
| 3 | 12 | 3 / 12 x 100 | 25% |
| 7 | 20 | 7 / 20 x 100 | 35% |
| 45 | 60 | 45 / 60 x 100 | 75% |
| 90 | 72 | 90 / 72 x 100 | 125% |
The Reverse Question: Finding the Whole
Sometimes you know the part and the percentage, but need the whole. Rearrange the formula:
Whole = Part / (Percentage / 100)
Example: 45 is 30% of what number? 45 / 0.30 = 150.
Check: 45 / 150 x 100 = 30%. Correct.
Connection to Other Percentage Questions
This formula is one of three core percentage calculations. The others are finding a percentage of a number (see how to calculate percentage of a number) and finding percentage change (see percentage change between two numbers). The percentage calculator on this site handles all three.
Frequently Asked Questions
What is the formula for finding what percent one number is of another?
Part / Whole x 100. For example, 45 is what percent of 180? 45 / 180 x 100 = 25%.
How do I know which number is the part and which is the whole?
The whole is the total or reference value. The part is the portion you are expressing as a percentage of it. In "18 is what percent of 90?", 90 is the whole and 18 is the part.
Can the answer be more than 100%?
Yes. If the part is larger than the whole, the percentage exceeds 100. For example, 120 is 150% of 80.
How do I express a test score as a percentage?
Divide your raw score by the total possible marks, then multiply by 100. Scored 68 out of 80? 68 / 80 x 100 = 85%.