sumivo

Proportion Calculator

Solve a : b = c : x for x.

01 / inputs

a
b
c

02 / result

X

6

Proportion
1 : 2 = 3 : 6
X
6

Calculation trace

  1. x = (2 × 3) ÷ 1 = 6
    6
    Cross multiplication
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How it works

A proportion a/b = c/x is solved for the unknown by cross-multiplication: x = (b × c) ÷ a.

Assumptions & limits

  • The first term a cannot be zero.
  • Assumes the two ratios are genuinely equal.
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FAQ

Which value does it solve for?
It solves for x in a/b = c/x. Arrange your known values so the unknown is the fourth term.
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Related calculators

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SOURCES

  • OpenStax, Rice University
    Prealgebra 2e ↗

    Solving proportions by cross-multiplication: a/b = c/x gives x = b·c ÷ a

    Accessed 2026-08-23