SPECIFICATION: Outdoor Dining Patio, Pergola Base, Storage Shed

12×12 Concrete Slab Calculator (Bags & Ready-Mix)

A 12×12 slab covers 144 square feet. At 4 inches deep, it requires 1.78 net cubic yards (1.96 cubic yards with 10% waste buffer). Requiring 88 bags of 80 lb mix, this sits right on the threshold between DIY mixing and ordering a short-load ready-mix truck.

SLAB DIMENSIONS144 SQ FT
THICKNESS (INCHES)4" Depth
+10%
DIY Retail Bag Weight:
Live Structural Cross-Section
12' × 12' Slab (4" Depth)
Structural cross-section of 12' x 12' concrete slab4" CONCRETE4" #57 STONE#4 REBAR @ 18" O.C.10 MIL VAPOR BARRIERCOMPACTED SUBGRADESPAN: 12 FT × 12 FT
Net Volume:1.78 cu yds
Order (+Waste):1.96 cu yds
Base Prep:4" Crushed Base
Reinforcement:#4 @ 18" O.C.
Yield Comparison (12' × 12')
DIY RETAIL STORE PICKUP
89 Bags
80 lb bags (~3 full pallets)
Dry Weight:7,120 lbs
Est. Bag Cost:$579
COMMERCIAL READY-MIX
1.96 cu yds
1 mixer truck (3500 PSI)
Delivery Scale:Short-Load Fee (<3 yds)
Est. Ready-Mix:$406

Frequently Asked Questions: 12×12 Concrete Slab Calculator (Bags & Ready-Mix)

How many bags of concrete for a 12x12 slab 4 inches thick?

A 12x12 slab at 4" depth requires 88 bags of 80 lb concrete with 10% waste. If using 60 lb bags, you will need 118 bags.

Is it cheaper to buy bags or call a concrete truck for a 12x12 slab?

88 bags of 80 lb concrete cost roughly $570 at retail home improvement centers. A ready-mix truck delivery for 2 cubic yards costs around $320-$400 for the concrete, but local batch plants often assess a $100-$150 short-load fee for orders under 3 yards.

How thick should a 12x12 patio slab be?

Standard residential patios, pergolas, and walking areas should be 4 inches thick. If you plan to park a heavy riding lawnmower or large hot tub (>4,000 lbs), increase thickness to 5 or 6 inches.