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Math Calculators

Proportion Calculator

Verified formula Updated Jun 2026 Private — runs on your device

Enter details
Verified formula Private

x (where a/b = c/x)

12.0000

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Proportion Calculator

The Proportion Calculator works out your x (where a/b = c/x) in an instant. Enter a, b and c and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

  1. Enter the a.
  2. Enter the b.
  3. Enter the c.
  4. Read off your x (where a/b = c/x) — the calculator updates automatically, with no button to press.

Formula

The Proportion Calculator uses the formula:

x (where a/b = c/x) = b × c ÷ a

Worked example

For example, with a of 2, b of 3 and c of 8, the x (where a/b = c/x) is 12.0000.

Inputs used
a 2
b 3
c 8
Results
x (where a/b = c/x) 12.0000

Results are estimates for educational use, not professional advice.

Frequently asked questions

Cross-multiply: for a/b = c/x, the missing x equals b × c ÷ a. With a = 2, b = 3 and c = 8, x is 12.

A proportion states that two ratios are equal. Solving it finds the unknown that keeps both ratios in balance.

They are used for scaling recipes, maps, models and any situation where quantities keep the same ratio.

Cross-multiplication divides by a, so a must be non-zero. A value of zero there has no valid solution.

The Proportion Calculator uses the formula: x (where a/b = c/x) = b × c ÷ a. For example, with a of 2, b of 3 and c of 8, the x (where a/b = c/x) is 12.0000.

Enter the a. Enter the b. Enter the c. Read off your x (where a/b = c/x) — the calculator updates automatically, with no button to press.

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