A ratio calculator scales A:B when you know one side. Search phrases include ratio calculator and proportion calculator for recipes, maps, and mixture problems.
The Formula Behind the Ratio Calculator
If A:B = a:b, then targetB = targetA × b ÷ a (and symmetrically for targetA).
When This Calculator Helps
Recipe doubles, map scales, and simple proportion word problems.
Using the Calculator
- Enter the values labeled in the tool above.
- Read the result cards — they update as you type.
- Cross-check one example by hand using the formula in this section.
- Open a related calculator below if your question needs a different formula.
Mistakes to Avoid
- Swapping A and B
- Mixing units inside a single ratio without converting
Getting the Most Out of It
- Simplify first with the Fraction Calculator
More Calculators to Try
Where the Estimate Falls Short
Results are estimates for learning and planning. They are not loan offers, tax filings, payroll determinations, or professional advice. Review our disclaimer.