How many 80 lb bags of concrete to pour a 4ft by 4ft by 5 inch thick?

To calculate the number of 80 lb bags of concrete needed for a 4ft by 4ft area at 5 inches thick, first determine the volume in cubic feet. The volume is 4ft x 4ft x (5/12)ft = 6.67 cubic feet. An 80 lb bag of concrete typically yields about 0.6 cubic feet, so you would need approximately 11 bags (6.67 ÷ 0.6 ≈ 11.11). Thus, you'll need 11 bags of concrete.