Ratio to Percentage Calculator
This ratio to percentage calculator handles both readings of a ratio: A out of B, where 3 out of 4 is 75%, and A to B as shares of a total, where 3:4 is 42.86% and 57.14%. It also shows the simplified ratio and the decimal.
How to use the ratio to percentage calculator
- Choose the reading. Use A out of B when B is the whole and A is part of it. Use A : B share of the total when A and B are two separate parts that together make the whole.
- Enter the two numbers. They do not have to be whole numbers, and they do not have to be simplified first.
- Read the result. The first mode returns one percentage. The second returns two, one for each part, and they add to 100%.
- Check the simplified ratio and the decimal shown underneath. 18:24 simplifies to 3:4, and the decimal form is what the percentage is built from.
If you are unsure which mode a question wants, the next section gives a one-line test that settles it.
The two formulas
A : B as shares: A’s share = A ÷ (A + B) × 100
Both are the same operation applied to a different denominator, and picking the denominator is the whole job. Once you have the decimal, multiplying by 100 finishes it, which is what the decimal to percent calculator does on its own.
Worked through with 3 and 4:
The two answers are far apart, and neither is wrong. They answer different questions about the same pair of numbers.
Which reading does your question want?
Here is the test: does the second number include the first?
- Yes, B contains A. This is part-to-whole. “3 out of 4 dentists” means 4 dentists in total, 3 of whom agree. Use A out of B and you get 75%.
- No, A and B are separate. This is part-to-part. “Mix concentrate to water 1:4” means 1 part concentrate plus 4 parts water, 5 parts in all. Use the share mode and the concentrate is 20% of the drink.
The wording usually gives it away. “Out of”, “of the”, and “in every” signal part-to-whole. A colon, the word “to”, and the word “parts” signal part-to-part. Odds work the same way as parts: odds of 3:1 mean three losses for every one win, so the win rate is 1 ÷ 4 = 25%, not 33%.
Contexts that are almost always part-to-part: mixing and dilution ratios, aspect ratios, gear ratios, recipe ratios, odds, and any split of money or shares between people. Contexts that are almost always part-to-whole: survey results, test scores, hit rates, attendance and anything phrased as a fraction.
| Ratio | As “A out of B” | A’s share of A:B | B’s share | Total parts |
|---|---|---|---|---|
| 1:1 | 100% | 50% | 50% | 2 |
| 1:2 | 50% | 33.33% | 66.67% | 3 |
| 1:3 | 33.33% | 25% | 75% | 4 |
| 1:4 | 25% | 20% | 80% | 5 |
| 1:5 | 20% | 16.67% | 83.33% | 6 |
| 1:9 | 11.11% | 10% | 90% | 10 |
| 2:3 | 66.67% | 40% | 60% | 5 |
| 3:4 | 75% | 42.86% | 57.14% | 7 |
| 3:5 | 60% | 37.5% | 62.5% | 8 |
| 4:5 | 80% | 44.44% | 55.56% | 9 |
Read the 1:9 row carefully. As “1 out of 9” it is 11.11%; as a 1:9 split it is 10%. The gap of just over one percentage point is small enough to slip past a proofreader and large enough to matter.
Worked examples
Example: 18 correct answers out of 24
The 24 includes the 18, so this is part-to-whole.
75%. The simplified 3:4 is easier to sanity-check: three quarters is obviously 75%.
Example: splitting $4,200 in the ratio 3:4
Here the parts are separate, so the total is 7 parts, not 4.
Always add the shares back to the original total. If they do not reach it, you divided by one of the parts instead of by the sum.
Example: a 2:5 dilution
Two parts syrup to five parts water.
In a 350 ml glass that is 100 ml of syrup and 250 ml of water. Note it is not 40% syrup, which is what you get by mistakenly dividing 2 by 5.
Converting a percentage back to a ratio
Going the other way, a percentage becomes a ratio in three steps: write it over 100, simplify, then decide whether you want part-to-whole or part-to-part.
part-to-part: p : (100 − p), simplified
Example: 62.5% as a ratio
So 62.5% is 5 out of 8, or a 5:3 split. Check: 5 ÷ 8 = 0.625, and 5 ÷ (5 + 3) = 0.625. That decimal step is the same one the percent to decimal calculator does.
Percentages with awkward decimals often come from thirds and sevenths, and they simplify neatly once you recognize them. 33.33% is 1:3 as a whole and 1:2 as a split. 42.86% is 3:7 and 3:4. 66.67% is 2:3 and 2:1. If the percentage is over 100, the ratio is top-heavy: 150% is 3:2, which as a fraction is the improper 3/2, handled by the improper fraction calculator.
Ratios with three or more parts
The share method extends directly. Add all the parts to get the total, then divide each part by that total.
Example: 2:3:5
Example: a 1:2:4 concrete mix
One part cement, two parts sand, four parts gravel.
For a 21 kg batch: 3 kg cement, 6 kg sand, 12 kg gravel.
Doing it by hand, three habits keep you out of trouble. Simplify the whole ratio first by dividing every part by the greatest common divisor — 6:9:15 all divide by 3 to give 2:3:5, which is much easier to work with. Clear any fractions or decimals by multiplying every part by the same number, so 0.5:1:2.5 becomes 1:2:5. And always add your percentages at the end: if they do not come to 100, you have divided by a part instead of the total, or dropped one.
Note that a three-part ratio has no “A out of B” reading at all. With three or more parts, the share interpretation is the only one available.
Common mistakes
- Using B as the denominator in a part-to-part ratio. A 1:4 mix is 20% of the first ingredient, not 25%. The total is 5 parts.
- Using the total in a part-to-whole question. 3 out of 4 is 75%, not 42.86%.
- Reading odds as a fraction. Odds of 3:1 against mean a 25% chance, not 33%.
- Forgetting to multiply by 100. 3 ÷ 4 is 0.75, and 0.75 is 75%. Dropping that step gives 0.75%, which is a hundred times too small.
- Simplifying only one side. Both parts have to be divided by the same number. 18:24 becomes 3:4, not 3:24.
- Reversing the order. A ratio is ordered. 3:4 and 4:3 are different splits, 42.86% and 57.14%.
- Mixing units. A 1:3 ratio of grams to kilograms is not 1:3 of anything useful. Convert first.
- Expecting rounded shares to add to exactly 100. Thirds and sevenths never will.
Frequently asked questions
What is 3 out of 4 as a percentage?
75%. Divide the part by the whole and multiply by 100: 3 ÷ 4 = 0.75, so 75%. This is the part-to-whole reading, where the 4 already includes the 3. Read as a 3:4 split into separate parts it would instead be 42.86%, so check which question you are answering.
What is the ratio 3:4 as a percentage?
It depends on the reading. As two shares of a total of 7 parts, the first is 3 ÷ 7 = 42.86% and the second is 4 ÷ 7 = 57.14%. As “3 out of 4” it is 75%. Use the share reading when the parts are separate, such as splitting money, and the out-of reading when the second number is the whole.
How do I convert 1:5 to a percentage?
As a mixing or split ratio, the total is 6 parts, so the first is 1 ÷ 6 = 16.67% and the second is 83.33%. As “1 out of 5” it is 20%. Mixing instructions almost always mean the first reading: 1:5 concentrate to water is 16.67% concentrate.
What is 60% as a ratio?
3:5 as a part-to-whole ratio, or 3:2 as a split. Write it over 100 to get 60:100, then divide both by 20 to get 3:5. Against the remaining 40% it is 60:40, which divides by 20 to give 3:2. Check either one: 3 ÷ 5 = 0.6, and 3 ÷ (3 + 2) = 0.6.
How do I turn 2:3:5 into percentages?
Add the parts to get the total, then divide each by it. 2 + 3 + 5 = 10, so the shares are 20%, 30% and 50%. They add to 100%, which is the check. A ratio with three or more parts has no “out of” reading, so the share method is the only one that applies.
Does a ratio have to add up to 100%?
The shares of a part-to-part ratio always do, because every part is divided by the same total. A part-to-whole percentage does not, since it describes only one quantity. Rounded shares can land on 99.99% or 100.01% when the exact values repeat, as thirds and sevenths do.
What is 1:1 as a percentage?
As a split it is 50% and 50%, since the total is 2 parts. As “1 out of 1” it is 100%. A 1:1 ratio means equal amounts of two things, so a 1:1 syrup mix is half syrup and half water. The 100% reading only makes sense if the second number is the whole quantity.
How do I simplify a ratio before converting it?
Divide every part by their greatest common divisor. 18:24 both divide by 6 to give 3:4. If any part is a decimal or fraction, multiply everything by the same number first: 0.5:1:2.5 becomes 1:2:5 when multiplied by 2. Simplifying does not change the percentages, it just makes the arithmetic easier to check.
Are odds of 3:1 the same as 75%?
No. Odds of 3:1 against mean three losing outcomes for every one winning outcome, four outcomes in total, so the chance of winning is 1 ÷ 4 = 25%. Odds are part-to-part, not part-to-whole. Odds of 3:1 on would mean the opposite, a 75% chance. Add the two numbers before dividing.
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