Concrete Slab Cost by Size: 10x10 to 40x60, With Yards, Bags and 2026 Prices

A 20 × 20 concrete slab at 4 inches thick needs 4.94 cubic yards of concrete, about 5.3 yards with an 8% waste allowance. At typical 2026 ready-mix prices of $160 to $195 a yard, the concrete alone costs roughly $850 to $1,050 before delivery fees, base, reinforcement and labor.

Below are the same numbers for the slab sizes people ask about most, plus what the totals leave out.

How to calculate concrete for a slab

• Volume: length × width × thickness in feet, divided by 27 to get cubic yards.
• Waste: 8%, which covers subgrade variation, spillage and over-excavated edges. Use 5% on a well-formed slab and 10% on rough ground.
• Bags: 80 lb bags at 0.6 cubic feet each, with the same 8% waste.
• Concrete price: $160 to $195 per cubic yard delivered within the plant's normal zone, a common planning range for standard mixes in 2026. Your local price can sit outside it.

4-inch slabs (patios, walkways, garage floors)

• 10 × 10 (100 sq ft): 1.23 yd³, 1.33 yd³ with waste. About 61 bags. Concrete $213 to $260.
• 12 × 12 (144 sq ft): 1.78 yd³, 1.92 yd³ with waste. About 87 bags. Concrete $307 to $374.
• 16 × 20 (320 sq ft): 3.95 yd³, 4.27 yd³ with waste. Concrete $683 to $832.
• 20 × 20 (400 sq ft): 4.94 yd³, 5.33 yd³ with waste. Concrete $853 to $1,040.
• 24 × 24 (576 sq ft): 7.11 yd³, 7.68 yd³ with waste. Concrete $1,229 to $1,498.
• 30 × 40 (1,200 sq ft): 14.81 yd³, 16.0 yd³ with waste. Concrete $2,560 to $3,120.
• 40 × 60 (2,400 sq ft): 29.63 yd³, 32.0 yd³ with waste. Concrete $5,120 to $6,240.

6-inch slabs (shops, driveways with heavier vehicles, equipment floors)

• 10 × 10: 1.85 yd³, 2.0 yd³ with waste. Concrete $320 to $390.
• 20 × 20: 7.41 yd³, 8.0 yd³ with waste. Concrete $1,280 to $1,560.
• 24 × 24: 10.67 yd³, 11.52 yd³ with waste. Concrete $1,843 to $2,246.
• 30 × 40: 22.22 yd³, 24.0 yd³ with waste. Concrete $3,840 to $4,680.
• 40 × 60: 44.44 yd³, 48.0 yd³ with waste. Concrete $7,680 to $9,360.

Going from 4 to 6 inches adds 50% to the concrete. On a 30 × 40 shop slab, that is 8 more yards.

What the concrete number leaves out

The concrete is usually less than half of an installed slab. A complete slab estimate also carries:

• Short-load and delivery fees. Anything under the plant's minimum load, often 8 to 10 yards, can carry a fee of $50 to $250 or more. That hits every 4-inch slab on this list up to 24 × 24.
• Base stone. A 4-inch compacted gravel base under a 30 × 40 slab is about 15 cubic yards of stone, roughly 20 to 22 tons depending on the material.
• Reinforcement. Wire mesh, or #4 rebar at 18 or 24 inches each way, plus chairs.
• Vapor barrier under interior slabs.
• Forms, edge thickening and any turned-down footings. A monolithic slab with thickened edges can add several yards to the plain slab numbers above.
• Pump if the truck cannot reach.
• Finishing labor, saw cutting, curing and sealing.

Most published installed prices land between about $6 and $10 per square foot for standard residential slab work, but that range swings with region, access, thickness and finish.

Check before you order

1. Measure thickness at several points on the prepared subgrade. Half an inch of extra depth on a 30 × 40 slab is almost 2 more yards.
2. Ask the plant for its minimum load and short-load terms.
3. Round your order up to the nearest quarter or half yard. Running short and paying for a second truck costs far more than a little extra.

If you are bidding a slab off plans and need the full quantity takeoff, including base, rebar, vapor barrier and thickened edges, send us the plans.