Ratio Calculator

What is a ratio?

A ratio compares two quantities — like 2 cups of flour to 1 cup of sugar, or a 16:9 screen. Ratios that represent the same relationship are called equivalent, and a proportion is simply a statement that two ratios are equal. This calculator handles both everyday jobs: finding a missing term in a proportion, and reducing a ratio to its simplest whole numbers.

Solving proportions

When you scale a recipe, resize an image or convert a map distance, you're solving a proportion. Enter the three values you know in the A : B = C : D row and the calculator cross-multiplies — A × D = B × C — to work out the one you don't.

Simplifying ratios

Big numbers hide the underlying relationship. Simplifying divides both terms by their greatest common divisor so 1920 : 1080 becomes the familiar 16 : 9. The "X : 1" view normalises against the second term, which is the quickest way to compare two ratios directly.

Frequently asked questions

How do I solve a proportion?

Fill in three of the four boxes in the A : B = C : D row and leave one empty. The calculator cross-multiplies to find the missing value, so if you know A, B and C it solves for D, and so on.

How does simplifying a ratio work?

Enter both terms in the simplify row. The tool finds the greatest common divisor of the two numbers and divides both by it, giving the smallest whole-number ratio that means the same thing — for example 8 : 12 becomes 2 : 3.

Can I use decimals?

Yes. Both tools accept decimals. When simplifying, decimal inputs are scaled up to whole numbers first, then reduced, so 1.5 : 3 simplifies cleanly to 1 : 2.

What is the X : 1 result?

It expresses the ratio relative to a single unit of the second term, which makes two ratios easy to compare at a glance. A ratio of 16 : 9 is shown as about 1.7778 : 1.

Is my data private?

Yes. All calculations run in your browser. Nothing you type is sent anywhere.