Ratio Calculator
Simplify a ratio or solve a proportion, with the decimal and percentage.
This ratio calculator does two jobs. In Simplify mode it reduces a ratio like 1920 : 1080 to its lowest terms, and also expresses it as a decimal and in the handy “1 : n” form. In Solve mode it fills in the missing value of a proportion, so if a : b = c : x you get x instantly.
A ratio compares two quantities, and simplifying it means dividing both sides by their greatest common divisor. A proportion sets two ratios equal to each other, which is the classic “cross-multiply” problem from school: x = b × c ÷ a. Both are used constantly for aspect ratios, recipes, scale drawings, and mixing.
How to use it
- 1Choose “Simplify” to reduce a ratio, or “Solve proportion” to find a missing term.
- 2In Simplify, type the two parts (A and B). In Solve, type A, B and C for a : b = c : x.
- 3Read the results — the simplified ratio, decimal and 1 : n form, or the missing value x, all update as you type.
Frequently asked questions
How do I simplify a ratio?+
Divide both numbers by their greatest common divisor (GCD). For 1920 : 1080 the GCD is 120, so it reduces to 16 : 9. The calculator does this automatically in Simplify mode.
How do I solve a proportion for the missing number?+
For a : b = c : x, cross-multiply: x = b × c ÷ a. For example 1 : 2 = 5 : x gives x = 2 × 5 ÷ 1 = 10. Use Solve mode and enter A, B and C.
What does the “1 : n” form mean?+
It rescales the ratio so the first term is 1, which makes it easy to compare. A ratio of 4 : 10 becomes 1 : 2.5, telling you the second quantity is 2.5 times the first.
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