Let's assume that the mortar is negligible {probably not a good assumption}.... and the post is "solid"
Each brick is 3.5 inches by 6 inches by 3.5 inches = (7/24)ft x (1/2) ft x (7/24)ft = 49/1152 cu ft
And the post is 3.25 ft x 2.5 ft x 2.5 ft = (13/4) ft x (5/2) ft x (5/2) ft = 325 /16 cu ft
So.......to find the number of bricks needed, we have ( 325/16 ) / (49 / 1152) = about 478 bricks
