Proportion Solver

A proportion is a statement that two ratios are equal. Written as A/B = C/D, it means the relationship between A and B is the same as the relationship between C and D. Proportions are fundamental in mathematics and appear in everyday situations like scaling recipes, maps, and unit conversions. See also our use the Cubic Yard Calculator.

Enter three known numeric values into any three of the four fields (A, B, C, D) and type 'x' into the field whose value you want to find. The solver will automatically apply cross multiplication to compute the missing value. Exactly one field must contain 'x'.

Cross multiplication works by multiplying the numerator of one ratio by the denominator of the other. For A/B = C/D, you get A × D = B × C. Rearranging this equation lets you isolate whichever variable is unknown. For example, if x is in place of C, then x = (A × D) / B.

Two quantities are directly proportional when they increase or decrease together at the same rate — doubling one doubles the other. They are inversely proportional when one increases as the other decreases, such that their product stays constant. This solver handles direct proportions of the form A/B = C/D. You might also find our Aspect Ratio useful.

Yes. The solver accepts x in any single position — A, B, C, or D. The cross multiplication formula is rearranged automatically depending on which position holds the unknown, so you always get the correct result regardless of where x appears.

The constant of proportionality is the fixed ratio that relates two proportional quantities. In A/B = C/D, the constant k = A/B = C/D. Knowing this constant lets you predict any value in the proportional relationship once one value is given.

Yes. You can enter decimal numbers such as 1.5, 0.75, or 3.14 into any of the fields. The solver handles decimal inputs and returns a decimal result. If you need to work with fractions, convert them to their decimal equivalents before entering them.

Proportions appear in many everyday contexts: scaling a recipe (if 2 cups of flour make 12 cookies, how much flour makes 30 cookies?), map reading (1 cm = 50 km), currency exchange, and mixing paint colors. Any situation where two ratios must stay equal involves a proportion.