Enter the distance from A to C, the distance from B to D, and the distance from B to C into the Cross Ratio Calculator. The calculator will evaluate and display the Cross Ratio.

## Cross Ratio Formula

The following formula is used to calculate the Cross Ratio.

CR = (AC*BD) / ( BC * AD)
• Where CR is the Cross Ratio
• AC is the distance from A to C
• BD is the distance from B to D
• BC is the distance from B to C
• AD is the distance from A to D

## How to Calculate Cross Ratio?

The following example problems outline how to calculate Cross Ratio.

Example Problem #1

1. First, determine the distance from A to C.
• The distance from A to C is calculated to be : 4.
2. Next, determine the distance from B to D.
• The distance from B to D is measured to be: 6.
3. Next, determine the distance from B to C.
• The distance from B to C is found to be: 7.
4. Next, determine the distance from A to D.
• The distance from A to D is found to be: 10.
5. Finally, calculate the Cross Ratio using the formula above:

CR = (AC*BD) / ( BC * AD)

The values given above are inserted into the equation below and the solution is calculated:

CR = (4*6) / ( 7 * 10) = .3428 ( )

Example Problem #2

The variables required for this problem are provided below:

distance from A to C = 8

distance from B to D = 9

distance from B to C = 10

distance from A to D = 4