Proportion Calculator
Solve proportions and find the missing value quickly and accurately.
Enter any three values. Leave exactly one field empty to calculate the missing value. The proportion is written as A ÷ B = C ÷ D.
Proportion Result
What Is a Proportion?
A proportion is an equation showing that two ratios are equal. It can be written in the following form:
When three values are known, the Proportion Calculator can find the fourth missing value using cross multiplication.
How to Solve a Proportion
Suppose you have the following proportion:
Cross multiplication gives:
2D = 24
D = 12
Therefore, the missing value is 12.
Proportion Formula
For the proportion A ÷ B = C ÷ D, the missing value can be found using cross multiplication:
B = (A × D) ÷ C
C = (A × D) ÷ B
D = (B × C) ÷ A
Example of a Proportion
3 ÷ 6 = 9 ÷ D
3 × D = 6 × 9
3D = 54
D = 18
Therefore, the missing value is 18.
Where Are Proportions Used?
Proportions are commonly used in mathematics, cooking, recipes, measurements, maps, scale drawings, construction, science, finance and many everyday calculations.
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Frequently Asked Questions
What is a proportion calculator?
A proportion calculator finds an unknown value when two ratios are equal and three of the four values are known.
How many values do I need?
Enter three known values and leave exactly one value empty. The calculator will find the missing value.
Can I use decimal values?
Yes. Decimal numbers such as 2.5, 4.75 and 10.25 are supported.
What formula is used?
The calculator uses cross multiplication to solve A ÷ B = C ÷ D.
Can I use zero in a proportion?
A denominator in a proportion cannot be zero. The calculator checks the values to prevent invalid division by zero.
Is this Proportion Calculator free?
Yes. The calculator is free to use directly in your web browser without installing additional software.