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Cross Multiplication Calculator

Work out cross multiplication instantly with clear inputs, formula shown and shareable results.

About Cross Multiplication Calculator

Two equal ratios satisfy ad = bc, the cross product. Solving that for the unknown gives d = bc/a, and the two ratios should then agree exactly.

Formula

Cross multiplication

a/b = c/d ⇒ ad = bc ⇒ d = bc / a

Worked example

With the default values below, Cross Multiplication Calculator returns Value of d of 12.00000000. Change any input above and every figure here is recalculated in your browser.

Inputs used

a in a/b = c/d
3
b
4
c
9

Results

Value of d
12.00000000
b × c
36.00000000
a / b
0.75000000
c / d (should match a/b)
0.75000000

Step by step

  1. 1Values used
  2. 2Cross multiplication
  3. 3Value of d= 12.00000000
  4. 4b × c= 36.00000000
  5. 5a / b= 0.75000000
  6. 6c / d (should match a/b)= 0.75000000

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 8 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

If 3/4 = 9/d?

d = 4 × 9 / 3 = 12, and both ratios equal 0.75.

Why is cross multiplication valid?

Multiplying both sides of the equation by bd clears the denominators, leaving ad = bc.

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