Fractions to Percentages (and Back)
Level 2 Fractions · Reviewed by The NumThink editorial team · Last reviewed
Short version: Make the denominator 100: 3/5 = 60/100 = 60%. Know the key ones by heart: 1/2 = 50%, 1/4 = 25%, 1/5 = 20%, 1/10 = 10%.
This page is part of the NumThink Fractions course. Read why the method works, watch it run on worked examples, then drill it in the practice box below until it feels automatic.
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No signup · instant feedbackWhy it works
Percent means "out of 100", so a percentage is simply a fraction with 100 on the bottom. Multiply top and bottom of 3/5 by 20 and you get 60/100 — which is 60%.
Another way to see it: multiply the fraction by 100. 3/5 × 100 = 60, so 3/5 is 60%.
The steps
- Find what turns the denominator into 100. 3/5: 5 × 20 = 100.
- Multiply the numerator by the same number. 3 × 20 = 60.
- That numerator is the percentage. 3/5 = 60/100 = 60%.
Worked examples
Easy 3/4 = ?%
Show the thinking
4 × 25 = 100
3 × 25 = 75
So 3/4 = 75%.
Answer: 75
Medium 7/20 = ?%
Show the thinking
20 × 5 = 100
7 × 5 = 35
So 7/20 = 35%.
Answer: 35
Hard 35% = ?/20
Show the thinking
35% = 35/100
Divide top and bottom by 5: 35/100 = 7/20
So 35% = 7/20.
Answer: 7
When to use it
- Comparing scores: 17/20 is 85%, which beats 21/25, which is 84%.
- Any denominator that divides 100: 2, 4, 5, 10, 20, 25 and 50.
When NOT to use it
- Thirds and most sixths never give a whole-number percentage (1/3 is 33.3…%) — remember 1/3 as about 33% and 2/3 as about 67%.
- Odd eighths give half a percent (1/8 is 12.5%) — worth knowing, but not a whole-number answer.
Common mistakes
Reading the numerator as the percentage. Saying 3/5 is 3% or 35%. Fix: Scale the bottom to 100 first: 3/5 = 60/100 = 60%.
Scaling only the bottom. Turning 7/20 into 7/100 and answering 7%. Fix: Multiply the top and the bottom by the same number: ×5 gives 35/100, so 35%.
Check yourself: Sanity check against one half: 7/20 is less than 1/2, so it must be less than 50% — and 35% is ✓.