Proportion Calculator
Solve any proportion by entering three known values to find the missing fourth value. This calculator uses cross multiplication to solve proportions of the form a/b = c/d instantly.
A proportion is an equation stating that two ratios are equal: a/b = c/d. Solving proportions is essential in scaling recipes, converting units, working with maps and blueprints, and solving percentage problems.
Cross Multiplication
The fundamental method for solving proportions is cross multiplication: a x d = b x c. If any one value is unknown, you can solve for it algebraically.
For example, if 3/4 = x/20, cross multiply: 3 x 20 = 4 x x, so 60 = 4x, giving x = 15.
Verification
To verify a proportion is correct, check that the cross products are equal. If a x d equals b x c, the proportion is valid. This calculator automatically verifies every solution.