12x12 concrete slab
For a 12 by 12 foot slab at 4 inches thick, you need about 89 bags of 80 lb concrete mix, costing about $532.22.
Concrete slab
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Bags needed
8980 lb bags
= 118 x 60 lb bags
About $532.22 in 80 lb bags
= 1.78 cu yd ready-mix
Avg US retail price, checked Aug 2026.
If you are pouring a driveway, consider 6 inches thick. At that thickness, you will need about 132 bags of 80 lb mix.
This slab needs about 1.78 cubic yards, and you order ready mix concrete in cubic yards.
Bag prices are a US average, last checked Aug 2026.