Ratio Calculator

Simplifies a ratio a:b to its smallest whole-number form and, optionally, solves the missing value in a proportion a:b = c:d.

Enter a and b to see the simplified ratio. To solve a proportion, also fill in c and leave d blank (or fill in d and leave c blank) — the calculator solves for whichever field is empty.

A ratio of 4:6 simplifies to 2:3. Solving 4:6 = 10:d with c = 10 gives d = b × c / a = 6 × 10 / 4 = 15.

Simplification divides a and b by their greatest common divisor. Solving the proportion uses d = b × c / a when d is blank, or c = a × d / b when c is blank.

The greatest common divisor is found from the rounded absolute values of a and b, so whole-number ratios are the reliable case — decimal inputs are accepted but the simplified output may not be mathematically minimal.

b cannot be zero, since a ratio can't have a zero second term. Setting a to zero can make a solved proportion value non-finite. Non-integer results display to two decimal places.

Calculations run locally in your browser; the values you enter are not uploaded.