18x18 concrete slab
For a 18 by 18 foot slab at 4 inches thick, you need about 199 bags of 80 lb concrete mix, costing about $1,190.02.
Concrete slab
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Bags needed
19980 lb bags
= 264 x 60 lb bags
About $1,190.02 in 80 lb bags
= 4 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 298 bags of 80 lb mix.
This slab needs about 4 cubic yards, and you order ready mix concrete in cubic yards.
Bag prices are a US average, last checked Aug 2026.