Calculate the whole when you know a part and the percentage it represents. This is the app’s free “a is %b of c” calculator.
If a is b% of c, then a = (b/100) × c. Rearranging the equation gives c = a × 100 ÷ b. The known percentage must be different from zero.
| Question | Answer |
|---|---|
| 30 is 20% of what? | 150 |
| 45 is 15% of what? | 300 |
| 75 is 25% of what? | 300 |
Try these values in the calculator above.
Calculate the missing whole when a known amount represents a known percentage. In “30 is 20% of what number?”, 30 is the part, 20 is the percentage and the missing total is 150.
The equation uses the percent as a decimal: part = (percentage ÷ 100) × whole. Rearrange it to get whole = part ÷ (percentage ÷ 100). Dividing 30 by 0.20 gives 150. Check the answer by taking 20% of 150: the result is the original part, 30.
In the app, this free mode is called “a is %b of c.” Enter the known part as a and the numeric percentage as b. The result is c.
If 90 represents 15% of a budget, the full budget is 90 ÷ 0.15 = 600. If a commission of 120 is exactly 4% of a sale, the sale value is 120 ÷ 0.04 = 3,000. Both examples recover a whole from one of its proportional parts.
If 42 correct answers represent 70% of the questions, the total number of questions is 42 ÷ 0.70 = 60. This assumes each question carries the same weight and the percentage has not been rounded.
A rounded input can produce a total that is not a whole number. If 33 is described as 33% of a group, the result is 100; if that share was rounded from one third, the actual group size could differ. Use the most precise percentage you have.
25% equals one quarter. If 75 is one quarter of the total, multiply 75 by 4 to get 300. Similarly, 20% is one fifth, so a part of 30 corresponds to a whole of 30 × 5 = 150. These fraction equivalents let you solve simple examples without a calculator.
Keep track of what is missing. This page takes a part and a percentage and returns the whole. If you already know both the part and the whole, use the percentage of total calculator to find the rate.
To recover a price after a 20% discount, the price left is 80% of the original. For example, 80 ÷ 0.80 = 100. The reverse percentage app feature covers increases and decreases directly.
A known share of 0% cannot identify a unique whole. Dividing by zero is undefined. A share above 100% is mathematically valid: if 150 is 125% of a reference amount, that reference amount is 120.
Find a total from a known part and percentage with the app’s free “a is %b of c” mode.
This mode finds a total from a known part and share. To reverse a 20% discount, the final amount represents 80% of the original price. The dedicated reverse-percentage feature explains that specific task.
Yes. Find the whole is the app’s free “a is %b of c” mode. The free version has ads; Premium unlocks the other calculators and removes ads.
Ordinary results use up to eight decimal places. Very small or large results use scientific notation. The ≈ symbol marks display rounding, and the formula preserves the significant digits of your input values.
150. Convert 20% to 0.20, then divide 30 by 0.20. Check: 150 × 0.20 = 30.
Enter 20 in the Percentage field. The calculator converts it to 0.20 as part of the formula. Entering 0.20 would mean 0.20%, which is a different rate.
Yes. For example, if 12.5 is 2.5% of a total, the whole is 12.5 × 100 ÷ 2.5 = 500.
