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Calculators
Proportion Calculator - Solve a/b = c/d
Proportion Calculator - Solve a/b = c/d
Solve proportions by finding the missing value in the equation a/b = c/d
Calculators
Calculator
Reset
A
B
C
D
Calculate
Reset
How to Use
1
Enter three of the four values: a, b, c, and d
2
Leave exactly one field empty — that is the value to solve for
3
Click Calculate to find the missing value and see the full proportion equation
Frequently Asked Questions
What is a proportion?
A proportion is an equation stating that two ratios are equal: a/b = c/d. For example, if 2/4 = x/8, then x = 4.
How does the calculator find the missing value?
It uses cross multiplication. For a/b = c/d: if d is missing, d = (b × c) / a. The same logic applies for any missing variable.
What if I enter all four values?
If all four values are entered, the calculator will verify whether the proportion holds and tell you if the equation is valid or not.
Can proportions have negative numbers?
Yes, proportions can include negative numbers. The calculator handles negative values correctly.