Ratio Calculator
Solve proportions and simplify ratios.
- Simplified A : B
- 3 : 4
- Scale factor
- 3
How this calculator works
Enter three parts of a proportion A : B = C : D and the calculator finds D by cross-multiplying.
Formula
D = B × C ÷ A
Example
3 : 4 = 9 : D gives D = 12.
When to use it
- Scaling recipes and mixtures
- Resizing images and maps
- Splitting costs in a set ratio
Frequently asked questions
How do I scale a recipe with ratios?
Set A and B to the original amounts and C to the new amount of one ingredient. D gives the matching amount of the other.
Can ratios use decimals?
Yes. The calculator accepts decimals and shows the simplest whole-number ratio when both parts are whole numbers.
Learn more
Percentage change vs. percentage difference: which one should you use?
They sound the same and give different answers. Here is when to use percentage change, when to use percentage difference, and why it matters.
How to calculate ratios: simplify, scale and split amounts with confidence
How to simplify ratios, solve proportions and use ratios for recipes, shared costs and screen sizes, with worked examples.
How to simplify fractions: three methods, from quick to foolproof
Three reliable ways to reduce a fraction to lowest terms, including a method that works on any numbers, however large.