Cross multiplication calculator
Solve a proportion a/b = c/x (or a/b = x/d) by cross-multiplying.
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Tool guide
Cross multiplication calculator: how it works
Practical information to understand the result and use this tool correctly.
About Cross multiplication calculator
Cross multiplication converts a/b = c/d into a·d = b·c.
Choose which of a, b, c, or d is unknown; the rest must be filled.
Standard for rates, similar figures, and recipe scaling.
How to use it
- 1Select the unknown letter.
- 2Enter the three known values.
- 3Calculate the missing term.
Frequently asked questions
- Zero denominator?
- Undefined — proportions need non-zero denominators in context.
- Can values be negative?
- Yes, algebraically; interpret signs in your problem context.