3 : 4 = 9 : ?
4 × 9 ÷ 3 = 12.
Ratio Calculator
Solve a proportion for the missing value, or simplify a ratio to its lowest terms.
Result
Enter your values and select Calculate to see the result.
Result
Enter your values and select Calculate to see the result.
Runs in your browser — nothing you enter is sent to a server.
How the Ratio Calculator works
Solve A : B = C : ? finds the missing value in a proportion — useful for scaling recipes, maps and image sizes. Simplify a ratio reduces a ratio to its lowest whole-number terms, such as a screen resolution to its aspect ratio. Decimal ratios like 1.5 : 2 are scaled up to whole numbers first.
Formula
D = B × C ÷ A
Where:
- A
- First term of the known ratio
- B
- Second term of the known ratio
- C
- First term of the new ratio
This is cross-multiplication: A × D = B × C.
Examples
Simplify 1920 : 1080
Both divide by 120, giving 16 : 9.
Frequently asked questions
How do I scale a recipe with a ratio?
If a recipe for 4 uses 300 g of flour and you're cooking for 6, solve 4 : 300 = 6 : ? to get 450 g.
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