A percent is a fraction with denominator 100: 80% means 80 out of every 100, which is 80/100 = 4/5. To write it as a fraction in lowest terms, put the number over 100 and divide the top and bottom by their greatest common factor (GCF, also called the GCD or HCF). If the number has decimals, first multiply the numerator and denominator by a power of 10 that clears them, then simplify. For the opposite direction, from a fraction to a percent, use fraction to percent.
Worked example: 12.5% as a fraction
A tank is 12.5% full. What fraction of the tank is that?
- Write the percent over 100 and clear the decimal point. You get 12.5/100. There is one decimal place, so multiply the top and bottom by 10 to get 125/1000.
- Find the GCF. The GCF of 125 and 1000 is 125.
- Divide the top and bottom by 125. 125 ÷ 125 = 1 and 1000 ÷ 125 = 8.
Result: 1/8 of the tank.
Check: 1/8 × 100 = 12.5, which is the percent you started with.
How to simplify and check the result
Simplifying means dividing the numerator and denominator by the same number, and the value does not change. The opposite step, multiplying both by the same number to build up an equivalent fraction, also keeps the value, which is why 125/1000 and its reduced form stand for the same percent. The equivalent fractions calculator shows both steps, and the greatest common divisor calculator gives you the divisor that reduces in a single step. When the GCF is 1, the fraction is already in lowest terms and stays as it is.
To check a conversion, multiply the fraction by 100 and compare with the original percent. With 2/5 × 100 = 40 you get back to the 40% you started with, because multiplying by 100 undoes the division by 100.
Common conversions
The table gathers everyday percents with their fraction in lowest terms. The odd multiples of 12.5%, such as 37.5%, give eighths (3/8), and percents over 100% give improper fractions, which can also be written as a mixed number.
| Percent | Over 100 | Fraction in lowest terms |
|---|---|---|
| 0.5% | 0.5/100 = 5/1000 | 1/200 |
| 5% | 5/100 | 1/20 |
| 7% | 7/100 | 7/100 |
| 10% | 10/100 | 1/10 |
| 25% | 25/100 | 1/4 |
| 37.5% | 37.5/100 = 375/1000 | 3/8 |
| 40% | 40/100 | 2/5 |
| 75% | 75/100 | 3/4 |
| 150% | 150/100 | 3/2 = 1 1/2 |
| −20% | −20/100 | −1/5 |
Thirds and sixths are not listed here because their percents repeat; you will find them in the fraction, decimal and percent table.
Repeating percents
A repeating percent, or one with a fraction inside it, such as 33 1/3%, cannot be typed in the box. Only terminating percents are accepted. Work it out by hand using the first question below.
Other pages, depending on what you have
If you have a decimal without the % sign, use decimal to fraction. To find a part of an amount with the fraction you got, there is fraction of a number. And if you need a discount, an increase, or what percent one amount is of another, the percentage calculator solves it directly. OpenStax covers converting between percents, fractions, and decimals with more examples (accessed October 17, 2026).
Frequently asked questions
How do you convert a repeating percent like 33 1/3% to a fraction?
Work it out by hand: 33 1/3% is 100/3 divided by 100, which gives 1/3. Another way is to move the point: 33.3̅% equals the decimal 0.3̅, which the repeating decimal to fraction calculator turns into 1/3. With 33.33% you get 3333/10000, which differs from 1/3 by 1/30000.
What fraction is 0.25%, and how is it different from 0.25?
0.25% = 0.25/100 = 25/10000 = 1/400, one part in 400. The decimal 0.25 without the sign is 1/4, which is 25%. The two differ by a factor of one hundred, which matters with interest and fees, where mixing them up changes the result a hundredfold.
How do I type a decimal percent like 62.5%, and what about commas?
Use a period: 62.5% and 62.5 % give the same fraction, 5/8, and the space before the sign is optional. A comma only groups thousands, so 1,250% is read as 1250% and gives 25/2. A decimal comma such as 12,5% is rejected with a message asking for a period.
How do I use the fraction to find 15% of an amount?
Convert 15% to 3/20 and multiply by the amount: 3/20 of 80 is 3 × 80 ÷ 20 = 12. The fraction of a number calculator does this with any fraction, and the percentage calculator handles discounts and increases directly.