Ratio Calculator
Simplify a ratio to lowest terms, or solve A : B = C : D for the missing value.
Simplifying a ratio
Divide both sides by their greatest common divisor: 12 : 18 has gcd 6, so it reduces to 2 : 3. Decimals work by scaling first: 2.5 : 1.5 becomes 25 : 15, which reduces to 5 : 3. The 1 : n form (here 1 : 1.5) is often the most readable for comparisons like student-teacher ratios or map scales.
Solving a proportion
A : B = C : D → D = B × C / A
Cross-multiplication: if 12 servings need 18 eggs, 10 servings need 18 × 10 / 12 = 15. The same one-liner handles recipe scaling, currency at a known rate, paint mixing and similar-triangle problems.