About the Ratio Calculator
Ratios turn up in recipes, screen dimensions, model scales, mixing paint, and every proportion question in school maths. This tool reduces a ratio to its simplest whole-number form and solves the classic "A is to B as C is to what" proportion for the missing term.
How to use the Ratio Calculator
- Enter the two parts of your ratio to see it simplified.
- Switch to proportion mode to solve for a missing term.
- Fill in any three of the four values; the fourth is calculated for you.
- Use the decimal equivalent to check scaling quickly.
The formula behind it
A ratio is simplified by dividing both terms by their greatest common divisor. In a proportion A:B = C:D, the missing term follows from A × D = B × C.
Frequently asked questions
What is the difference between a ratio and a fraction?
A fraction compares a part with the whole; a ratio compares parts with each other. In a 2:3 mix there are five parts in total, so the first ingredient is 2/5 of the mixture, not 2/3.
How do I scale a recipe with this?
Use proportion mode. If the recipe serves 4 and you need 7, enter 4 : ingredient amount = 7 : unknown, and the tool returns the new quantity.
How do I find a screen aspect ratio?
Enter the pixel width and height and simplify. 1920 × 1080 reduces to 16:9, and 2560 × 1080 reduces to 64:27, the ultrawide format.
Can a ratio have decimals?
It can, but whole numbers are conventional. Multiply both terms by 10 or 100 until the decimals disappear, then simplify.