Cross Multiplication
Fill in three terms and solve for the fourth.
Result
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Enter numbers to see the result.
Cross product
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Check
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Formula: For a/b = c/d, cross multiplying gives a x d = b x c. Divide to isolate the unknown term.
Solve a proportion like a/b = c/x. Pick which term is unknown and the calculator cross multiplies to find it.
Fill in three terms and solve for the fourth.
Enter numbers to see the result.
In the proportion a/b = c/d, multiplying both sides by the denominators gives a x d = b x c. That single equation lets you solve for any one unknown term by dividing the cross product by the known value on the same side.
Proportions show up in unit conversion, scale drawings, recipe scaling, currency math, and similar triangles. If two ratios are equal and you know three of the four numbers, cross multiplication finds the fourth.