Math July 13, 2026 · 8 Min Read

Cross Multiplication Calculator – Guide & Formulas

Solve proportions and compare fractions using cross multiplication. Enter any proportion to find the unknown value with clear step-by-step work.

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Put these formulas into practice with our instant, step-by-step Cross Multiplication Calculator.

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Solve proportions and compare fractions using cross multiplication. Enter three known values in a proportion to find the unknown, or compare two fractions to see which is larger.

Key Takeaway

Use the free Cross Multiplication Calculator to solve proportions and compare fractions using cross multiplication. enter any proportion to find the unknown value with clear step-by-step work. Get instant results with step-by-step explanations.

How to Use the Cross Multiplication Calculator

  1. Enter values for the proportion a/b = c/d, leaving one field empty for the unknown.
  2. The calculator identifies which variable is missing and solves automatically.
  3. Review the cross multiplication steps showing a×d = b×c.
  4. For fraction comparison, enter two fractions to see which is larger using cross products.

The Formula

Cross multiplication: If a/b = c/d, then a × d = b × c. To solve for an unknown, isolate it: x = (known product) / (remaining value).

Variable Definitions

  • a, b: The numerator and denominator of the first fraction
  • c, d: The numerator and denominator of the second fraction
  • a × d: The first cross product (numerator × opposite denominator)
  • b × c: The second cross product (denominator × opposite numerator)

Solving 3/8 = x/24

Find the unknown value x using cross multiplication.

  1. Step 1: Set up the proportion: 3/8 = x/24.
  2. Step 2: Cross multiply: 3 × 24 = 8 × x.
  3. Step 3: Calculate left side: 72 = 8x.
  4. Step 4: Solve for x: x = 72 / 8 = 9.
  5. Step 5: Verify: 3/8 = 0.375 and 9/24 = 0.375 —

Frequently Asked Questions