How Much Concrete for a 30x30 Slab? (4 Inch Thick)

A 30 × 30 ft slab poured 4 inches thick needs 12.22 cubic yards of concrete, including 10% extra for spillage and uneven ground. That's 550 bags of 80 lb premix or 734 bags of 60 lb.

Change any number below to match your project. The concrete calculator works for any size.

What are you pouring?
For a footing, use its width, e.g. 1' 4"
Patios and walks: 4 in. Driveways: 5–6 in.
5–10% is typical

Enter your measurements to see the result.

How it's worked out

  1. Area: 30 × 30 = 900 sq ft
  2. Volume: 900 sq ft × 4 in ÷ 12 = 300 cu ft
  3. Add 10%: 300 × 1.1 = 330 cu ft
  4. Cubic yards: 330 ÷ 27 = 12.22 yd³
  5. 80 lb bags: 330 ÷ 0.6 cu ft per bag = 550 bags

30x30 slab at other thicknesses

ThicknessCubic yards80 lb bags60 lb bags
4 in12.22550734
5 in15.28688917
6 in18.338251100

4 inches suits patios, sheds and walkways. Driveways and garage floors usually get 5 to 6 inches.

At 12.22 yards, ready-mix delivery is usually cheaper and much less work than mixing 550 bags by hand. Most suppliers deliver in quarter or half yard steps, so round up when you order.

Other common sizes

More detail: How Many Bags of Concrete Do I Need? (Chart + Examples)