Ratio Calculator

What do you want to do?

How it works

Simplifying divides both parts by their greatest common divisor — the same trick as simplifying a fraction. 12 : 18 divides by 6 to become 2 : 3, and the relationship between the parts is unchanged.

Scaling multiplies both parts by the same factor. To scale 2 : 3 so the first part becomes 10, the factor is 10 ÷ 2 = 5, giving 10 : 15. Recipes, mixing ratios, and map scales all work this way: change one part, and the factor tells you the other.

Proportions state that two ratios are equal: a : b = c : x. Cross-multiplying gives x = (b × c) ÷ a. So if 3 : 6 = 5 : x, then x = (6 × 5) ÷ 3 = 10 — and indeed 5 : 10 simplifies to the same 1 : 2.

Aspect ratios are just width : height simplified. A 1920 × 1080 screen simplifies by 120 to 16 : 9 — the standard for HD and 4K displays. A 1024 × 768 screen is 4 : 3, the old TV shape. The decimal form (width ÷ height) is handy for comparing shapes that do not simplify to familiar numbers.

Frequently asked questions

What is the aspect ratio of 2560 × 1440? Divide both by 160: 16 : 9 — the same shape as 1920 × 1080, just more pixels. Resolution changes size; the aspect ratio is only about shape.

Can a ratio have decimals? Yes. 1.5 : 2.5 is a perfectly good ratio; simplifying first clears the decimals (multiply both by 10) and then reduces, giving 3 : 5. This calculator handles decimal parts that way automatically.

How do I write a ratio as "1 : n"? Divide both parts by the first part. 2 : 3 becomes 1 : 1.5. The mirror form "n : 1" divides both parts by the second part instead. Both are shown with the simplified result.