You fill in any three of the four fields (A, B, C, D) and leave one blank. The calculator uses cross-multiplication — A × D = B × C — to solve for the missing value. It also computes the GCD of A and B to produce a simplified ratio. If fewer than three values are provided, no solution is shown. Non-integer inputs are displayed as decimal ratios rather than simplified whole numbers.
If A/B = C/D, then A × D = B × C. This is the fundamental property of proportions. Rearranging this equation lets you solve for whichever value is missing.
Yes, the calculator accepts decimal inputs. Fraction inputs need to be converted to decimals first (e.g., enter 0.5 instead of 1/2). The simplified ratio output works best with whole-number inputs.
The calculator needs at least three values to solve for the fourth. With two or more blanks, there are infinite solutions, so no result is displayed.
Common uses include scaling recipes, converting map distances to real distances, calculating ingredient proportions, resizing images, mixing paint colors, and solving proportion word problems in math class.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.