Concrete slab cost by size

Why cost per square foot is a lie at small sizes

A contractor quoting $4–$8 per square foot is pricing their day, not a material identity. Ready-mix has a short-load fee below about 4 cubic yards — $50–$150 for sending a truck that is not full. 12 of the 20 sizes on this site sit under that threshold. A mixer rental is ~$70 whether you mix 20 bags or 80. Forms lumber follows the perimeter, not the area, so a long thin 10×20 pays more wood per square foot than a 16×16.

That is why a 10×10 slab at 100 sq ft shows materials around $298 ($2.98/sq ft of mix) while a 20×20 slab at 400 sq ft shows $908 ($2.27/sq ft). Four times the area is not four times the ticket. The DIY vs hire page is the labour argument; this page is why the material column itself is not a straight line.

Bags beat a truck on 0 of these sizes — the pads. Past that, the short-load fee still hurts, but mixing 88 bags for a 12×12 slab is a worse slab than a truck for less money. 3 sizes on this site are genuine bag jobs; treat the rest as truck jobs that happen to have a bag number printed for comparison.

Every size we publish, at 4 inches

80 lb bags, 10% waste, ready-mix rounded up to the quarter yard. Click through for joints, mesh takeoff, and the written context for that footprint.

Slab	Area	80 lb bags	Ready-mix	Cheaper materials	DIY est.	Pro est.
8×8 slab	64 sq ft	40	1 yd³*	Truck ≈ $215 –$315	≈ $315–$615	≈ $256–$512
8×10 slab	80 sq ft	49	1.25 yd³*	Truck ≈ $256 –$356	≈ $356–$656	≈ $320–$640
8×12 slab	96 sq ft	59	1.5 yd³*	Truck ≈ $298 –$398	≈ $398–$698	≈ $384–$768
10×10 slab	100 sq ft	62	1.5 yd³*	Truck ≈ $298 –$398	≈ $398–$698	≈ $400–$800
10×12 slab	120 sq ft	74	1.75 yd³*	Truck ≈ $339 –$439	≈ $439–$739	≈ $480–$960
10×16 slab	160 sq ft	98	2.25 yd³*	Truck ≈ $421 –$521	≈ $521–$821	≈ $640–$1,280
10×20 slab	200 sq ft	123	2.75 yd³*	Truck ≈ $504 –$604	≈ $604–$904	≈ $800–$1,600
12×12 slab	144 sq ft	88	2 yd³*	Truck ≈ $380 –$480	≈ $480–$780	≈ $576–$1,152
12×14 slab	168 sq ft	103	2.5 yd³*	Truck ≈ $463 –$563	≈ $563–$863	≈ $672–$1,344
12×16 slab	192 sq ft	118	2.75 yd³*	Truck ≈ $504 –$604	≈ $604–$904	≈ $768–$1,536
12×20 slab	240 sq ft	147	3.5 yd³*	Truck ≈ $628 –$728	≈ $728–$1,028	≈ $960–$1,920
12×24 slab	288 sq ft	176	4 yd³	Truck ≈ $660	≈ $760–$960	≈ $1,152–$2,304
16×16 slab	256 sq ft	157	3.5 yd³*	Truck ≈ $628 –$728	≈ $728–$1,028	≈ $1,024–$2,048
16×20 slab	320 sq ft	196	4.5 yd³	Truck ≈ $743	≈ $843–$1,043	≈ $1,280–$2,560
20×20 slab	400 sq ft	245	5.5 yd³	Truck ≈ $908	≈ $1,008–$1,208	≈ $1,600–$3,200
20×24 slab	480 sq ft	294	6.75 yd³	Truck ≈ $1,114	≈ $1,214–$1,414	≈ $1,920–$3,840
24×24 slab	576 sq ft	352	8 yd³	Truck ≈ $1,320	≈ $1,420–$1,620	≈ $2,304–$4,608
24×30 slab	720 sq ft	440	10 yd³	Truck ≈ $1,650	≈ $1,750–$1,950	≈ $2,880–$5,760
30×30 slab	900 sq ft	550	12.25 yd³	Truck ≈ $2,021	≈ $2,121–$2,321	≈ $3,600–$7,200
30×40 slab	1,200 sq ft	734	16.5 yd³	Truck ≈ $2,723	≈ $2,823–$3,023	≈ $4,800–$9,600

*Short-load fee included in the truck column. Ask your supplier where their minimum sits — it is not always 4 yards.

The same footprints, grouped by how the job actually behaves

Pads (under 100 sq ft)

This is a bag-and-mixer pour: the excavation and the base take longer than the concrete.

• 8×8 slab — 40 bags / 1 yd³, materials ≈ $215 –$315
• 8×10 slab — 49 bags / 1.25 yd³, materials ≈ $256 –$356
• 8×12 slab — 59 bags / 1.5 yd³, materials ≈ $298 –$398

Patios and shed floors

Big enough to live on, small enough that the short-load fee still decides bags vs a truck.

• 10×10 slab — 62 bags / 1.5 yd³, materials ≈ $298 –$398
• 10×12 slab — 74 bags / 1.75 yd³, materials ≈ $339 –$439
• 10×16 slab — 98 bags / 2.25 yd³, materials ≈ $421 –$521
• 12×12 slab — 88 bags / 2 yd³, materials ≈ $380 –$480
• 12×14 slab — 103 bags / 2.5 yd³, materials ≈ $463 –$563
• 12×16 slab — 118 bags / 2.75 yd³, materials ≈ $504 –$604
• 16×16 slab — 157 bags / 3.5 yd³, materials ≈ $628 –$728
• 16×20 slab — 196 bags / 4.5 yd³, materials ≈ $743

Parking pads and short drives

Thickness and compacted base matter more than the bag count once wheels are involved.

• 10×20 slab — 123 bags / 2.75 yd³, materials ≈ $504 –$604
• 12×20 slab — 147 bags / 3.5 yd³, materials ≈ $628 –$728
• 12×24 slab — 176 bags / 4 yd³, materials ≈ $660

Shop floors and large pours

This is a truck pour. Budget joints, reinforcement, and labour before you budget bags.

• 20×20 slab — 245 bags / 5.5 yd³, materials ≈ $908
• 20×24 slab — 294 bags / 6.75 yd³, materials ≈ $1,114
• 24×24 slab — 352 bags / 8 yd³, materials ≈ $1,320
• 24×30 slab — 440 bags / 10 yd³, materials ≈ $1,650
• 30×30 slab — 550 bags / 12.25 yd³, materials ≈ $2,021
• 30×40 slab — 734 bags / 16.5 yd³, materials ≈ $2,723

What going to 6 inches costs, size by size

Thickness is the one upgrade that is almost always worth it if the slab will see a vehicle, and it is linear in volume. The extra is not linear in pain: on a pad it is a few more bags; on a 20×20 slab it is a bigger truck ticket. Ready-mix delta, 4″ to 6″, including the short-load fee where it still applies:

Slab	Extra materials, 4″ → 6″
8×8 slab	≈ $83
10×10 slab	≈ $124
12×12 slab	≈ $165
12×20 slab	≈ $198
16×20 slab	≈ $371
20×20 slab	≈ $454
24×24 slab	≈ $619
30×40 slab	≈ $1,320

The thickness guide is the decision; this table is the bill. Replacing a 4″ driveway that cracked under a truck costs many times the $454 it would have cost to pour the 20×20 slab at 6″ the first time.

What is not in these numbers

• Access. A backyard pad that needs a pump or a long barrow run is a different quote. The calculator cannot see your gate.
• Spoil removal. Excavated soil is bulky. The DIY-vs-hire page counts it; this materials table does not, because it is a site condition, not a bag yield.
• Decorative finishes, stamped patterns, colour. Those are multiplier jobs. The pro column is a basic broom-finish slab.
• Your region. Ready-mix in a coastal metro and ready-mix in the rural Midwest are not the same $165/yd³. Confirm with a supplier. Prices here are dated June 2026 national averages, re-checked quarterly.

For the sequence on a bag pour, see how to form and pour a small slab. For whether the aisle brand matters (it does not, on standard mix), see Quikrete vs Sakrete. For the labour call at five representative sizes, stay on DIY vs hiring a pro.