Enter a, b, and c for a : b = c : x.
Arithmetic Calculator
Ratio & Proportion Calculator
Simplify a two-part ratio and solve a missing fourth value in an equivalent proportion.
Instant answer
Formula breakdown
Browser-based
Mobile friendly
Interactive calculator
Enter your values
Use the example values or replace them with your own. Required validation happens before the calculation.
Ready
Calculated answer
Result
Simple workflow
How to use the Ratio & Proportion Calculator
Follow these steps to get a reliable result and understand how it was produced.
The calculator cross-multiplies the proportion.
View x and the simplified ratios.
Understanding the calculation
Cross multiplication converts the proportion into a simple equation. The first ratio is also reduced to lowest whole-number terms where possible.
a : b = c : x, so x = bc/aThe result panel substitutes your numbers into this relationship and shows the important intermediate values.
Common uses
- Scale drawings and maps
- Recipes and mixtures
- Rates, pricing, and resizing
Accuracy tips
- The first value a cannot be zero.
- Use values in matching units.
- Decimals are allowed, though whole values simplify most clearly.
Helpful answers
Ratio & Proportion Calculator FAQs
Important details about formulas, inputs, limitations, and result interpretation.
What is a proportion?
A proportion states that two ratios are equal.
How is the missing value found?
By cross multiplication: a×x = b×c, then x = bc/a.
Can ratios contain decimals?
Yes. The missing value calculation supports decimals.
Does order matter in a ratio?
Yes. Reversing the order changes the meaning of the comparison.