Ratio & Proportion Calculator
Enter a ratio to simplify it to its lowest terms, or fill in three of the four values in a proportion (A:B = C:D) to solve for the missing one — instant and exact.
Calculators Runs entirely in your browser
All calculations happen on your device — nothing is sent to a server.
What this tool does
Simplifies ratios and solves proportions: give it three terms and it finds the missing fourth in a : b = c : x.
When to use it
- Scaling a recipe from four people to ten at the same proportions.
- Working out a proportional dimension in a design or plan.
- Reducing a ratio to its simplest form.
- Solving a proportion problem for study or work.
How to use it
- Enter the "First term (a)" and "Second term (b)".
- Read the "Simplified ratio" if that is all you need.
- Enter the "Third term (c)" to solve a : b = c : x for the unknown.
A practical example
Input
a=2, b=3, c=10
Output
A simplified ratio of 2:3, and x = 15, because 2:3 = 10:15.
Limitations
- The third term is optional; without it you get the simplification only.
- Zero values in a dividing position make the proportion unsolvable.
- This handles a two-term ratio; compound ratios of three or more terms are not supported.
Privacy and processing
The ratio is worked out on your device and the terms are never sent anywhere.
Technical notes
- Simplification uses the greatest common divisor, and the proportion is solved by cross-multiplication.