A 80 lb bag of standard concrete mix yields about 0.6 cubic feet, so it takes roughly 45 bags to make one cubic yard. As a worked example, a 10×10 pad at 4 inches thick needs about 62 bags with a 10% waste allowance. The calculator above is pre-set to 80 lb bags; enter your dimensions or a known volume.
Common questions
How many 80 lb bags of concrete in a cubic yard?
About 45 bags. One cubic yard is 27 cubic feet and each 80 lb bag yields roughly 0.6 cubic feet. Past a yard, priced ready-mix delivery usually beats mixing bags on both cost and effort.
How many 80 lb bags for a 10x10 slab?
At 4 inches thick, about 62 bags including 10% waste. Use the calculator above to adjust the size and thickness to your pad.
How much area does one 80 lb bag cover?
At 4 inches thick, one bag covers about 1.8 square feet. Halve that for 8-inch-deep work like post holes and footing patches.