How many bricks in 864 sq foot wall?

That depends on the size of your brick, how many openings you have in the wall, do you have any details such as soldiers, coined corners ect.

You can get close by dividing the sq footage by the "lay-up" factor, how many bricks it takes per square foot. Then do not deduct footage for smaller Windows and door. This will cover waste and details. Example if your layup is 3.54 you would need 3059 bricks for your wall. 864 x 3.54 = 3058.56