Cross Multiplication Calculator
Compare A/B with C/D by calculating their two cross products. Both denominators, B and D, must be nonzero.
How to use Cross Multiplication Calculator
1. Enter A, B, C, D in the stated order. 2. Follow nonzero denominator and whole-number requirements where they apply. Keep corresponding quantities on the same unit scale. 3. Select Calculate or press Enter to see cross products. 4. Copy result copies the output; Reset clears the inputs and answer.
Why use this tool?
Check whether two supplied ratios form a proportion, with all four terms already known.
How the calculation works
For A/B = C/D, compare A × D with B × C. Equality is checked with exact decimal cross-products of the entered numeric text; displayed products use floating-point formatting. Numeric outputs use browser floating-point arithmetic, with six decimal places at most. Smaller nonzero outputs use six significant digits in scientific notation. Unrepresentable intermediate values or numeric outputs beyond the supported magnitude are rejected. Numeric input magnitudes, including each fraction or ratio component, must not exceed 9,007,199,254,740,991. Mathematical references: https://openstax.org/books/prealgebra-2e/pages/4-key-concepts and https://openstax.org/books/prealgebra-2e/pages/6-5-solve-proportions-and-their-applications.
Example
A = 1, B = 2, C = 2 and D = 4 give cross products 4 and 4, so the ratios are equal.
Practical tip
Use the missing-ratio tool when one term is unknown. A zero denominator cannot define a quotient.
Frequently asked questions
Why are B = 0 and D = 0 rejected?
A/0 and C/0 are undefined. Equal zero cross products do not establish that these undefined ratios are equal.
Do signed inputs always have a practical interpretation?
These forms perform the stated arithmetic. Negative values, rates above 100% or a negative baseline can be mathematically valid while being unsuitable for a particular real-world quantity. Check the task and model before applying the result.
Does the tool choose units or round my input first?
Enter corresponding measurements in matching units; the maths forms do not convert units automatically. Exact fraction and ratio text is kept for integer arithmetic. Other numeric operations use browser floating-point values and the display precision stated above.