Ratio Calculator
Solve A:B = C:D for any single missing value.
Enter three of the four values in the proportion A:B = C:D and the calculator solves for the fourth. Useful for scaling recipes, blueprints and conversions.
Common use cases
- Scale a recipe by computing the new ingredient amount
- Resize an image proportionally given target width or height
- Compute a missing dimension on a scaled blueprint
- Solve unit-conversion proportions in homework
Frequently asked questions
What's a proportion?▾
An equation showing two ratios are equal: A/B = C/D. Cross-multiply to solve: AD = BC.
Can I leave more than one blank?▾
No — the proportion has one degree of freedom. With two unknowns, infinite solutions exist.
Does it simplify ratios?▾
Not currently — it solves for missing values. For simplification, divide both sides by the GCD.