A fraction is really just a division waiting to happen. Converting one to a decimal takes a single step — and a little number theory tells you in advance whether the result will end neatly or repeat forever.
The basic method
Divide the numerator (top) by the denominator (bottom). So 3/4 means 3 ÷ 4 = 0.75, and 7/8 means 7 ÷ 8 = 0.875. That's the whole method — everything else is shortcuts and edge cases.
Common fractions worth memorizing
| Fraction | Decimal | Percent |
|---|---|---|
| 1/2 | 0.5 | 50% |
| 1/3 | 0.333… | 33.3% |
| 1/4 | 0.25 | 25% |
| 1/5 | 0.2 | 20% |
| 1/8 | 0.125 | 12.5% |
| 1/10 | 0.1 | 10% |
| 3/4 | 0.75 | 75% |
Terminating vs repeating decimals
Some fractions end (terminate), like 3/4 = 0.75. Others repeat forever, like 1/3 = 0.333… There's a simple rule: reduce the fraction to lowest terms, then look at the denominator. If its only prime factors are 2 and 5, the decimal terminates. If any other prime factor remains (3, 7, 11, …), it repeats.
- 1/8 → denominator 8 = 2×2×2 → terminates (0.125).
- 1/20 → denominator 20 = 2×2×5 → terminates (0.05).
- 1/3 → denominator 3 → repeats (0.333…).
- 1/6 → denominator 6 = 2×3 → repeats (0.1666…).
Fractions to percentages
Once you have the decimal, multiply by 100 to get a percentage: 3/4 = 0.75 = 75%. For the reverse and much more, see how to calculate percentages. Working with two quantities instead of one? The Ratio Calculator simplifies and solves proportions.