Proportion Calculator
Choose A, B, C, or D as the unknown in A/B = C/D, then enter the other three terms. The calculator isolates the selected position and validates both denominators.
How to use the Proportion Calculator
Enter the term to solve and the other three known values in A ÷ B = C ÷ D.
Review term order, units, nonzero denominators, sign, and whether direct proportionality is appropriate.
Read the solved missing value and completed proportion.
Formula
For a ÷ b = c ÷ d, cross multiplication gives a × d = b × c. Solve the missing term by isolating it, such as d = b × c ÷ a when a is nonzero.
Example
For 3/5 = 12/x, 3x = 60, so x = 20 and both ratios equal 0.6.
Assumptions and limitations
- The two ratios are asserted to be directly equivalent; uncertainty, nonlinear relationships, and sampling error are outside the model.
- Proportion Calculator treats the entered values as estimates and does not infer missing project, account, or personal details.
- Calculations retain working precision except where the cited method requires an intermediate rounding step; displayed values are then formatted separately. Source rules and dated rates must be rechecked when they change.
Sources
- OpenStax: College Algebra 2eAlgebraic, ratio, radical, equation, and function formulas. Reviewed 2026-08-14.
- OpenStax: Elementary Algebra 2eOfficial formula, rate, or program guidance used by this calculator. Reviewed 2026-08-14.
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Frequently asked questions
How does the Proportion Calculator work?
For a ÷ b = c ÷ d, cross multiplication gives a × d = b × c. Solve the missing term by isolating it, such as d = b × c ÷ a when a is nonzero.
What information should I enter in the Proportion Calculator?
Enter the term to solve and the other three known values in A ÷ B = C ÷ D, then verify term order, units, nonzero denominators, sign, and whether direct proportionality is appropriate.
What should I verify before using this Proportion Calculator result?
The two ratios are asserted to be directly equivalent; uncertainty, nonlinear relationships, and sampling error are outside the model.
Reviewed 2026-08-14 · any-missing-term-v2 · content-2026-08-14 · Trusty Calculator Editorial Team