Is Percent of What Calculator
When you know a part and what percent it represents, you can recover the whole. “30 is 20% of what?” — enter 30 and 20 and the answer (150) appears with the working.
X is P% of what?
Results update as you type.
- 30 is 20% of
- 150
Steps
- 20% = 0.2
- 30 ÷ 0.2 = 150
Worked example
Example: $18 is 15% of what bill?
- Convert 15% to 0.15
- Divide the part by the decimal: 18 ÷ 0.15 = 120
$18 is 15% of $120.
Formula
Whole = Part ÷ (Percent ÷ 100)
This is the percent formula Part = Percent × Whole solved for the whole.
Frequently asked questions
40 is what percent of 5?
40 ÷ 5 × 100 = 800%. Use the “X is what percent of Y” calculator for that form.
How do I find the original number before a percentage was taken?
Divide the known part by the percent as a decimal. If 45 students are 30% of a class, the class has 45 ÷ 0.30 = 150 students.
Is this the same as reverse percentage?
Close. Reverse percentage starts from a value after an increase or decrease (like a price with tax) and divides by 1 ± the percent.
Last reviewed October 17, 2026 · Calculations run in your browser; nothing you enter is sent to a server.