Solve for the missing value in a proportion by using cross multiplication.
Last updated: March 2026 | By ForgeCalc Engineering
Calculation Steps
Missing variable: d
A proportion says that two ratios are equal. If three of the four values are known, the fourth value can be found with cross multiplication.
Example: Solve 1/2 = 3/d, so d = 6.
How many blanks can I leave?
Only one blank variable can be solved at a time.
Can decimals be used?
Yes. Any finite real values are accepted.
What if one of the known values is zero?
Zero can be valid in some cases, but not when it would create division by zero.
Is cross multiplication always appropriate?
Yes, for standard proportions of the form a/b = c/d.
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