Proportion Calculator
Solve proportions quickly and find a missing value in an equivalent ratio.
Solve a proportion
Enter three known values and leave one field blank. The calculator will find the missing value.
First ratio
Second ratio
Example:
Enter 2, 3 and 8, then leave the last field blank.
The answer is 12.
Missing Value
—
How to solve a proportion
A proportion states that two ratios are equal. When three values are known, the fourth value can be found using cross multiplication.
a / b = c / d
→
a × d = b × c
Step-by-step calculation
1
Enter three known values
Enter the three numbers you know and leave
the missing value blank.
2
Cross multiply
Multiply the known values diagonally across
the proportion.
3
Divide to find the answer
Divide the cross product by the remaining
known value.
Example
Suppose you want to solve 2/3 = 8/x.
Proportion
2 / 3 = 8 / x
Cross multiply
2 × x = 3 × 8
Calculate
2x = 24
Divide
x = 24 ÷ 2
Answer
x = 12
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Note: This calculator is intended for general mathematical calculations. Check that your inputs are appropriate for the calculation you are performing.