How many bags of concrete do i need to do a 4 ft x 5 ft 4 in thick slab?

To calculate the number of bags of concrete needed for a slab measuring 4 ft x 5 ft with a thickness of 4 inches, first convert the dimensions to cubic feet. The volume is 4 ft x 5 ft x (4/12 ft) = 6.67 cubic feet. If using standard 80-pound bags of concrete, which yield about 0.6 cubic feet each, you would need approximately 11 bags (6.67 ÷ 0.6 = 11.11). It’s advisable to buy a few extra bags to account for spillage or other variables.