How to calculate the number of combinations for Chess960 positions Can someone derive how do we get the total number of 960 possible positions for Chess960?
You're counting the same position a couple of times and not including the rule that the bishops have to be on opposite colors.  (And possible that the king must be between the rooks.)

The actual number is 4 x 4 x (6 x 5) / 2 x 4

4 for the LSB

4 for the DSB

(6 x 5) / 2 for the two knights (halved due to account for the same type of piece being placed)

4 for the queen

1 due to the king must be between the rooks  (Without this rule, it would be (3 x 2) / 2 or 1440.)