Ratio calculator
Free online ratio calculator. Solve proportions, find the missing value in A:B = C:X easily and quickly.
Enter 3 values and leave one empty. The result will appear automatically.
Proportion formula
In a proportion A : B = C : D, the cross products are equal:
A × D = B × C
How it works
- 1
Enter 3 known values
Fill in three of the four fields A : B = C : D with the known values of the proportion.
- 2
Leave the unknown value empty
Leave blank the field you want to calculate: it can be any of the 4 positions, A, B, C or D.
- 3
Get the result
The tool automatically solves the proportion using the fundamental property A × D = B × C.
FAQ
How do you solve a proportion?
Use the fundamental property: the product of the means equals the product of the extremes. If A:B = C:D, then A×D = B×C. The unknown value is derived by dividing.
Can I find any of the 4 values?
Yes, you can leave any field empty (A, B, C or D) and the calculator will find the missing value.
Does it work with decimal numbers?
Yes, the calculator supports integers and decimals with precision up to 4 decimal places.
