Ratio Calculator

Enter a ratio A : B and a new first value C — the calculator solves for the matching second value X so the proportion stays the same.

A (first value)

B (second value)

C (new first value)

2 : 3 = 10 : X

X = 15

(3 × 10) ÷ 2 = 15

Equivalent ratio

10 : 15

Simplified A : B

2 : 3

Scale factor

×5

Formula: A : B = C : X → X = (B × C) ÷ A (cross-multiplication).

Frequently asked questions

How do I solve A : B = C : X?: Cross-multiply: X = (B × C) ÷ A. For 2 : 3 = 10 : X, X = (3 × 10) ÷ 2 = 15.
Can ratios use decimals?: Yes. Simplification is only shown for whole-number ratios.