What is a Ratio to Percentage Calculator?
A ratio compares two quantities, written as A:B. A percentage expresses a value out of 100. This calculator converts any ratio into an equivalent percentage so you can interpret proportions, splits, and shares more easily. It supports two common interpretations of a ratio, letting you pick the one that matches your problem.
How to use it
Enter the first term (A) and the second term (B) of your ratio. Then choose how you want the percentage measured: A as part of the whole treats A + B as 100%, while A relative to B treats B as the 100% baseline. Click calculate to see the percentage, the decimal fraction, and the denominator that was used.
The formula explained
When A is a part of a whole, the percentage is the part divided by the total, times 100: $$\text{Percentage} = \frac{\text{A}}{\text{A} + \text{B}} \times 100\%$$ For example, a 3:1 ratio means 3 parts out of 4 total, so A is 75%. When you want A measured against B, use $$\text{Percentage} = \frac{\text{A}}{\text{B}} \times 100\%$$ The same 3:1 ratio then gives 300%, because 3 is three times B.
Worked example
Suppose a class has a boys-to-girls ratio of 3:2. Using A as part of the whole: $$\frac{3}{3 + 2} \times 100 = \frac{3}{5} \times 100 = 60\%$$ So boys make up 60% of the class. Using A relative to B: $$\frac{3}{2} \times 100 = 150\%$$ meaning there are 50% more boys than girls.
FAQ
Which mode should I use? Use "part of whole" for shares or splits (e.g., what fraction of the total). Use "relative to B" to compare one quantity against another baseline.
Can the percentage exceed 100%? Yes — in "relative to B" mode, if A is larger than B the result is over 100%, which is correct.
What if B is zero? Division by zero is undefined, so the calculator returns 0 to avoid an error. Make sure your denominator is non-zero for a meaningful result.
