Concrete for a 30×40 Slab at 4" Thick

A 30 ft × 40 ft slab poured 4 inches thick is 1,200 sq ft and needs 14.81 cubic yards of concrete — order 16.00 CY to cover 8% waste, or about 720 80-lb bags for a small pour. Adjust the dimensions below for your project.

Concrete including allowance

16.00 cu yd

Slab area

1,200 sq ft

Concrete needed

14.81 cubic yards16.00 CY with 8% allowance

80-lb bags

720 bagsor 960 × 60-lb bags

Ready-mix cost (est.)

$2,800$175/CY sample price; delivery and short-load fees extra

How this estimate works

Volume = length × width × (thickness ÷ 12) ÷ 27, in cubic yards. The headline includes your waste allowance (8% by default); do not add it again. Bag counts round up using 0.60 cu ft per 80-lb bag or 0.45 cu ft per 60-lb bag. Confirm the product yield.

The shopping list uses ready-mix plus a sample 4-inch base, mesh, forms, and vapor barrier. These companion materials are starting allowances, not a structural specification. Verify your slab design, reinforcement, strength, and supplier delivery minimums.

Planning estimate. Adjust allowances and sample prices for your supplier; tax, delivery, and labor are not included.

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Concrete for a 30×40 Slab at 4" Thick

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