How many 80lbs of concrete mix for a 18x20x4 pad?

To calculate the amount of concrete mix needed for an 18x20x4 pad, first determine the volume in cubic feet: 18 ft × 20 ft × 4 ft = 1,440 cubic feet. Since a standard 80 lb bag of concrete mix yields about 0.6 cubic feet, you would need approximately 2,400 bags (1,440 ÷ 0.6 = 2,400). Therefore, you'll need around 2,400 bags of 80 lb concrete mix for the project.