Question 1

How many bags of concrete in a cubic yard?

Accepted Answer

About 60 bags of 80 lb mix or 90 bags of 60 lb mix make up one cubic yard. Bagged mix is cost-effective under ~1 cubic yard; above that, ready-mix delivery is usually cheaper.

Question 2

How thick should a concrete slab be?

Accepted Answer

Patios and walkways are typically 4 inches; driveways and garage floors 5–6 inches; heavy-load slabs 6+ inches with rebar. Thicker slabs use proportionally more concrete.

Question 3

How much does a concrete slab cost?

Accepted Answer

Materials for a plain slab run roughly $6.50–$10.50 per square foot poured, though the ready-mix itself is closer to $140 per cubic yard. This tool estimates the material cost; labour and finishing are extra.

Question 4

Should I add a waste allowance?

Accepted Answer

Yes — 5–10% is standard to cover spillage, uneven subgrade and over-excavation. Running short mid-pour causes cold joints, so it's better to slightly over-order.

Concrete Slab Cost Calculator: 12×12 at 4 inch thickness

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