Proportion Calculator

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Choose which term in a/b = c/d you want to find.
Direct: both ratios are equal (a/b = c/d). Inverse: the products are equal (a · b = c · d), used when one quantity increases as the other decreases.
Top-left term of the proportion.
Bottom-left term of the proportion.
Top-right term of the proportion.
Model a recipe scale, map distance, or unit-conversion scenario.
Missing term
12
Scale factor (c / a)3
Left ratio (a / b)0.75
Right ratio (c / d)0.75
Ratio difference0%
Equation3 / 4 = 9 / 12
Left ratio (a/b)0.75
Right ratio (c/d)0.75

D = 12

  • The missing term D = 12. Both ratios now equal 0.75, confirming the proportion is balanced.
  • The right-hand pair is 3x larger than the left, a scale-up factor of 200%.
  • The cross-product check passes: a x d equals b x c, so the ratios are exactly equal.

Next stepSwitch "Solve for" to find any of the other three terms using the same three inputs.

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