It seems like 5x5 inch squares is the norm for what is called a charm pack now.
I've seen squares available in various sizes - 1.5, 2, 2.5, 4, 4.5, 5, 5.5, 6, 6.5 inches.
It has puzzled me that the jelly rolls are 2.5 inches wide and the charm squares are 5 inches wide.
When the squares are 5 inches wide, it takes two strips 2.75 inches wide sewn together (1/4 inch seam) to equal 5 inches.
Two strips 2.5 inches wide sewn together (1/4 inch seam) end up being only 4.5 inches wide.