Cross Multiplication Calculator

Cross Multiplication is a method for solving proportions — equations where two fractions (ratios) are equal: a/b = c/d. By cross-multiplying, the equation becomes a × d = b × c, which can be solved for any unknown variable.

Cross multiplication is used in scaling recipes, map reading (scale factors), unit conversion, similar triangle calculations, mixture problems, and proportional reasoning in science and engineering.

The method works because if two fractions are equal, the cross products must be equal. This is the fundamental property of proportions.

If a/b = c/d, then a × d = b × c

To solve for an unknown:

• If solving for a: a = (b × c) / d
• If solving for b: b = (a × d) / c
• If solving for c: c = (a × d) / b
• If solving for d: d = (b × c) / a

Example: 3/4 = x/12 → 3 × 12 = 4 × x → 36 = 4x → x = 9