Ratio Calculator
Free ratio calculator. Simplify any ratio to its lowest terms, or solve for the missing value in a proportion A : B = C : D with a single unknown.
Ratio Input
Simplified Ratio
16 : 9
Details
How It Works
Choose a mode
Pick "Simplify" to reduce a ratio to lowest terms, or "Solve proportion" to find a missing value in A : B = C : D.
Enter your numbers
For Simplify, type the two parts of the ratio. For a proportion, fill in three of the four boxes and leave the unknown one blank.
Read the result
See the simplified ratio or the solved value instantly, along with the completed proportion and decimal equivalent.
A ratio compares two quantities and shows how many times one value contains another, written in the form A : B. Ratios are everywhere — in recipes, maps, mixing paint, financial analysis and screen aspect ratios — so reducing them to their simplest form makes them far easier to read and compare.
A proportion is a statement that two ratios are equal, such as A : B = C : D. Because the cross-products of a proportion are equal, you can solve for any single missing term. This calculator handles both jobs: it reduces a ratio to lowest terms using the greatest common divisor, and it solves a proportion for whichever value you leave blank.
Frequently Asked Questions
How do you simplify a ratio?
Divide both parts of the ratio by their greatest common divisor (GCD). For example, 12 : 8 has a GCD of 4, so it simplifies to 3 : 2. If the parts are decimals, this calculator first scales both sides up to whole numbers before reducing.
How do I solve a proportion with a missing value?
A proportion states that two ratios are equal: A : B = C : D, which means A/B = C/D. Cross-multiplying gives A·D = B·C, so any missing value can be found by rearranging — for example D = B·C / A. Leave exactly one of the four boxes blank and the calculator solves it.
Can this calculator handle decimal ratios?
Yes. When you enter decimals in Simplify mode, both numbers are multiplied by a power of ten so they become integers, and the result is then reduced by the greatest common divisor for a clean whole-number ratio.
What is an equivalent ratio?
Equivalent ratios represent the same relationship between two quantities. Multiplying or dividing both parts of a ratio by the same non-zero number gives an equivalent ratio — for instance 1 : 2, 2 : 4 and 5 : 10 are all equivalent.
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