To get the percentage of a number, multiply the number by the percentage (as a decimal) and you’re done.

Core idea

  • Formula:
    Percentage of a number = number×percent100\text{number}\times \frac{\text{percent}}{100}number×100percent​.
  • Example: 20% of 50
    • Convert 20% to decimal: 20%=20/100=0.220%=20/100=0.220%=20/100=0.2.
* Multiply: 0.2×50=100.2\times 50=100.2×50=10.

* So, 20% of 50 is 10.

Step‑by‑step method

  1. Take the percentage you want (say 15%).
  1. Divide it by 100 to turn it into a decimal (15 ÷ 100 = 0.15).
  1. Multiply that decimal by the number you care about (0.15 × 80 = 12).
  1. The result is the percentage of the number (15% of 80 is 12).

Another example: 30% of 200

  • 30% → 30 ÷ 100 = 0.3
  • 0.3 × 200 = 60
  • So 30% of 200 is 60.

Quick mental tricks

These shortcuts help you do it faster in your head.

  • 10% of a number: move the decimal one place left.
    • 10% of 470 → 47.
  • 1% of a number: move the decimal two places left.
    • 1% of 470 → 4.7.
  • 5% of a number: find 10% and halve it.
    • 10% of 240 is 24, so 5% is 12.
  • 25% of a number: divide by 4.
    • 25% of 80 → 80 ÷ 4 = 20.
  • 50% of a number: divide by 2.
    • 50% of 90 → 45.

You can combine these:

  • 15% of 200 = 10% (20) + 5% (10) = 30.
  • 35% of 80 = 25% (20) + 10% (8) = 28.

If you know the part and want the percent

Sometimes you know “part of a whole” and want to know what percent that is.

  • Formula:
    Percent = partwhole×100\dfrac{\text{part}}{\text{whole}}\times 100wholepart​×100.

Example: 15 out of 50

  • 15 ÷ 50 = 0.3
  • 0.3 × 100 = 30%
  • So 15 is 30% of 50.

Mini FAQ

  • “What is X% of Y?” → X100×Y\dfrac{X}{100}\times Y100X​×Y.
  • “X is what percent of Y?” → XY×100\dfrac{X}{Y}\times 100YX​×100.
  • “If P% of a number is N, what is the number?” → N×100P\dfrac{N\times 100}{P}PN×100​.

Think of percentages as “out of 100”: 40% means 40 out of 100, and calculating a percentage is just scaling your number down to that “out of 100” view.

TL;DR: Convert the percentage to a decimal by dividing by 100, then multiply by the number (e.g., 18% of 250 → 0.18 × 250 = 45).