How it works
The tool cross-multiplies valid proportions or divides corresponding terms to preserve equality. It may reduce ratios to lowest terms by dividing out common factors.
Formula
If a/b = c/d then ad = bc (cross products). Unknown x from a/b = c/x → x = (b × c) ÷ a
How to use Ratio & Proportion Calculator
- Enter the known ratio or three terms of a proportion.
- Specify which value is unknown if the layout asks.
- Submit and read the missing term and simplified ratio.
- Verify units match on both sides before trusting the result.
Worked examples
Concrete numbers and cases you can check against the tool above.
Recipe scale 6 → 10 servings
If 6 servings need 2 cups flour, set 6/2 = 10/x → x ≈ 3.33 cups. Keep cups on both sides of the proportion.
When to use Ratio & Proportion Calculator
Cross-multiplication is simple but error-prone with unit mismatches. The calculator keeps ratios consistent and flags zero denominators.
Common use cases
- Scale a recipe from 4 servings to 7.
- Convert map scale to real-world distance.
- Mix paint or chemical ratios for a larger batch.
- Check similar triangles in geometry homework.
Inputs and outputs
- Decimal or fractional terms
- Two-term ratios and four-term proportions
Privacy
This tool runs entirely in your browser. Your data never leaves your device — nothing is uploaded to our servers.
Frequently asked questions
- What if a denominator is zero?
- A ratio with zero on the bottom is undefined. The calculator should reject or warn rather than divide by zero.
- Can I enter fractions?
- Many proportion tools accept decimals; enter fractions as decimals or use a fraction form if the page provides it.
- Do units need to match?
- Corresponding terms should use the same units (miles with miles, cups with cups) or the proportion will not represent a real scale.