How much concrete do I need for a slab?

The formula is length × width × thickness (in feet), divided by 27 to convert cubic feet to cubic yards. For a 10×10 ft slab at 4 inches thick: 10 × 10 × 0.333 = 33.3 cubic feet ÷ 27 = 1.23 cubic yards. Always add 10% overage to account for spillage, uneven subgrade, and form movement. The concrete industry rule of thumb for a 4-inch slab: divide total square footage by 81 to get cubic yards.

For bagged concrete, each 80-lb bag yields 0.60 cubic feet (per Quikrete and Sakrete manufacturer specs). One cubic yard equals 45 bags of 80-lb mix, 60 bags of 60-lb mix, or 90 bags of 40-lb mix. For projects over 1 cubic yard, ready-mix delivery is typically more practical and cost-effective than hand-mixing dozens of bags.

What thickness should my concrete slab be?

Slab thickness depends on the intended use. Walkways and garden paths: 3–4 inches. Patios and standard residential slabs: 4 inches. Heavy-duty patios and driveways: 5–6 inches. Garage floors: 6 inches minimum. Structural foundations: 8+ inches (consult an engineer). Local building codes may specify minimum thickness, especially for driveways and garage slabs. Thicker slabs use more concrete but provide significantly better load-bearing capacity.

Do I need rebar or wire mesh in my concrete slab?

Wire mesh (6×6 W1.4) is standard for residential patios and walkways. It prevents surface cracking and holds the slab together if cracks develop. Rebar grid (#4 bars on 18-inch centers) provides stronger structural reinforcement for driveways, garage floors, and any slab supporting heavy loads. For a basic patio, wire mesh is sufficient. For a driveway or garage, rebar is recommended. Always place reinforcement on chairs or supports so it sits in the middle third of the slab thickness.

Frequently asked questions