Ratio Calculator
Simplify ratios to lowest terms or solve for a missing proportion.
Formula
About this calculator
Ratios show up everywhere — mixing paint or fuel, scaling a recipe, reading aspect ratios like 16:9, comparing odds, or splitting a bill by shares. This calculator handles the two things people actually need to do with them: simplify a ratio to its lowest terms, and solve a proportion when one of the four values is missing.
Simplifying works exactly like reducing a fraction: the calculator finds the greatest common divisor of both terms and divides through, so 16:9 stays 16:9 but 100:250 becomes 2:5. It also shows the ratio as a decimal, which is handy when you want to compare two ratios quickly or feed the value into another calculation.
The solve mode handles proportions of the form A:B = C:D where D is unknown. This is the classic 'scaling' problem — if a recipe uses 2 cups of flour for every 3 eggs and you have 10 eggs, how much flour? Enter 2, 3 and 10 and it returns the missing quantity via cross-multiplication.
For adding, subtracting, multiplying or dividing two fractions rather than comparing ratios, the fraction calculator is the better tool; for part-of-whole percentages, use the percentage calculator.
Frequently asked questions
How do I simplify a ratio?
Divide both sides of the ratio by their greatest common divisor. For example, 100:250 divides by 50 to become 2:5. The calculator does this automatically.
How do I solve a proportion with a missing value?
For A:B = C:D, cross-multiply: D = B × C / A. Enter the three known values in solve mode and the calculator returns the fourth.
Can a ratio be shown as a decimal?
Yes. Dividing the first term by the second gives the decimal form — for instance 16:9 is about 1.778 — which the calculator shows alongside the simplified ratio.