Other bag sizes
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Bag count
Concrete bag calculator
How many bags of concrete your slab needs — in the bag size you're buying, with every other size shown alongside.
Slab & bag size
FIG. 01required
required
required
Bag yields (set concrete): 80 lb = 0.60 ft³, 60 lb = 0.45, 50 lb = 0.375, 40 lb = 0.30. Counts round up — buy one or two spare.
You need
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That's — of concrete
How this is calculated
Find your slab volume in cubic feet (length × width × thickness), add a waste margin, then divide by the bag's yield: 0.60 ft³ for 80 lb, 0.45 for 60 lb. This calculator does it and shows every bag size at once.
bags = ⌈(length × width × thickness in ft × (1 + waste%)) ÷ bag yield⌉
Buying in bulk or pouring more than a yard? Check the bags-vs-ready-mix breakeven, or get a full material list from the cost estimator.
FAQ
How many bags of concrete do I need?
Find your slab volume in cubic feet (length × width × thickness), add a waste margin, then divide by the bag's yield: 0.60 ft³ for 80 lb, 0.45 for 60 lb. This calculator does it and shows every bag size at once.
How many 80 lb bags of concrete in a cubic yard?
About 45. One cubic yard is 27 cubic feet and an 80 lb bag yields 0.60 ft³, so 27 ÷ 0.60 = 45 bags. A 60 lb bag yields 0.45 ft³, giving 60 bags per yard.
When should I stop buying bags and order a truck?
Around 1 cubic yard. That's roughly 45 eighty-lb bags — about 3,600 lb to haul and mix by hand. Above that, ready-mix is usually cheaper and saves a full day of labor.