Cross Multiplication Calculator
Enter any 3 of the 4 values in a proportion and leave the value you want to find blank.
Cross Multiplication Calculator
Our Cross Multiplication Calculator solves proportions of the form a/b = c/d. Enter any 3 of the 4 values, leave the field you want to find blank, and click Calculate to instantly get the missing numerator or denominator, rounded to 6 decimal places.
Cross Multiplication Formula
Cross multiplication works by multiplying the numerator of one fraction by the denominator of the other. Once you know three of the four values, you can rearrange this equation to solve for the fourth:
Missing a: a = (b × c) ÷ d
Missing b: b = (a × d) ÷ c
Missing c: c = (a × d) ÷ b
Missing d: d = (b × c) ÷ a
Example Calculation
Solve for x: 2/5 = x/20
x = (2 × 20) ÷ 5 = 40 ÷ 5 = 8
So, 2/5 = 8/20
Who Can Use This Calculator?
👉 Try our Cross Multiplication Calculator to solve any proportion instantly.