Ratio Calculator
Simplify ratios and solve for the unknown term in a proportion A:B = C:D.
Ratio Calculator
Simplify ratios and solve for the unknown term in a proportion A:B = C:D.
Real-World Examples
A recipe uses 2 cups flour to 3 cups water. If you use 6 cups flour, how much water? 2:3 = 6:D
D = 9
On a map 1 cm = 50 km. How many km is 4 cm? 1:50 = 4:D
D = 200
A ratio of 3 parts red to 5 parts blue. If you use 9 parts red, how much blue? 3:5 = 9:D
D = 15
Common Mistakes to Avoid
Confusing which term is unknown
Fix: In A:B = C:D, if D is unknown you compute (B×C)/A. If C is unknown instead, compute (A×D)/B.
Not simplifying the ratio
Fix: Always divide both terms by their greatest common divisor to express the ratio in simplest form.
Treating a ratio as a fraction of the whole
Fix: A ratio 3:2 means 3 parts to 2 parts (5 total), not 3/2 of the whole. The whole is the sum of the parts.