30x30 Concrete Slab, 4 Inches Thick
A 30 × 30 ft slab (900 sq ft) at 4 in thick takes about 12.22 cubic yards of concrete, with 10% extra for waste. For ready-mix, order 12.25 cu yd for the 30x30, about $1,715 – $2,205 delivered. Bagged, the same 30x30 is 550 80 lb or 734 60 lb bags, about $3,670 – $5,138 for the concrete alone.
- Ready-mix order
- 12.25 cu yd
- Ready-mix cost
- $1,715 – $2,205
- 80 lb bags
- 550
- Bag cost
- $3,670 – $5,138
The 30x30 (4 in) prices are national material ranges as of 2026-09, not a quote from a supplier.
The 30x30 three-car garage or shop
Thirty feet square is a common size for a three-car garage, with three 9 ft doors or a 16 ft door plus a single, and storage along the back.
As a shop, 900 sq ft gives room for a car on a lift, a bench, a table saw and an open center to work on a project.
This pour runs past one ready-mix truck at 4 in, so the delivery has to be scheduled as two loads, with enough hands to finish 900 sq ft before it sets.
A 4 in 30x30 pour: check first
- Line up a finishing crew of at least three or four people for this area.
- Ask the building department about frost footings under the walls.
- If a lift is planned, see the 6 in version of this slab.
Full plan for a 30x30 slab, 4 in
- Area
- 900 sq ft
- Thickness
- 4 in
- Volume
- 12.22 cu yd
Bagged concrete estimate (DIY)
$4,542 – $6,557
Est. as of 2026-09 — not a live quote
Ready-mix delivered (materials only)
$1,715 – $2,205
Est. as of 2026-09 — not a live quote
For a pour this size, ready-mix delivery is typically more practical than mixing bags by hand.
Shopping list
- Concrete mix (60 lb bags) Or 1,100 × 40 lb, 880 × 50 lb or 550 × 80 lb bags. 734 bags
- Ready-mix concrete Alternative to bagged mix; most suppliers have a 1 cu yd order minimum. 12.25 cu yd
- Compactable gravel sub-base 4 in compacted base beneath the slab. 15 tons
- 6x6 welded wire mesh Reinforcement for crack control; not a substitute for engineered rebar on structural slabs. 990 sq ft
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Buy bagged concrete
Pick up bagged mix and reinforcement from a hardware store for smaller pours.
View shopping listAssumptions
- Waste allowance: 10% applied to account for over-excavation and spillage.
- Approx. wet weight: 49,500 lb (24.8 tons).
- Prices are national-average retail/delivery ranges as of 2026-09, not live quotes.
Bags or ready-mix for a 30x30 slab, 4 in?
12.25 cu yd for the 30x30 is 2 truckloads at 8 cu yd each (the conservative end of the 8 to 10 a truck carries), about $1,715 – $2,205. Ask the supplier to space the trucks so each load goes down before the last one stiffens (a wet edge), line up enough hands to place and finish 900 sq ft at 4 in, and ask about a pump if the truck can't reach every corner of the 30x30. Ready-mix wins for this 30x30 by roughly $2,444 (range midpoints), and nobody has to mix 550 bags by hand.
Is 4 in thick enough for a 30x30 slab?
Many residential garage floors the size of this 30x30 are poured 4 in thick, which clears the IRC minimum of 3-1/2 in for cars and light trucks. Go to 5 or 6 in if the 30x30 will hold heavy pickups, an RV, a car lift or a tractor, or sits on soft or clay soil, and check your local code first. At 6 in the same 30x30 takes about 18.33 cu yd. See also: 30x30 slab at 6 in.
Control joints for a 30x30 slab at 4 in
Like any slab, a 4 in 30x30 shrinks while it cures; control joints decide where its cracks go. ACI and PCA guidance spaces joints 24 to 36 times the thickness, which for this 30x30 at 4 in is every 8 to 12 ft, sawn 1 in deep (a quarter of the slab) once the surface holds up to the blade, usually within a day.
On the 30x30 at 4 in, a joint every 10 ft or less means 2 joints each way: 9 panels of about 10 × 10 ft and 120 ft of saw cut.
How much a 30x30 slab 4 in thick weighs
Wet concrete weighs about 150 lb per cubic foot, so the 30x30 pour is about 49,500 lb (24.8 tons). As bags, the 30x30 is 550 80 lb bags, 44,000 lb in all: about 30 trips in a pickup carrying 1,500 lb a load. Nobody hauls 44,000 lb of bags for a 30x30 in a pickup; it comes by ready-mix truck or as pallets on a delivery truck.
The 30x30 at 4 in against nearby sizes
Every row uses the same 10% waste and prices as the 30x30 at 4 in; costs are for the concrete only.
| Slab | Cu yd | 60 lb bags | 80 lb bags | Ready-mix order | Bags cost | Ready-mix cost |
|---|---|---|---|---|---|---|
| 20x40 slab, 4 in | 10.86 | 652 | 489 | 11 cu yd | $3,260 – $4,564 | $1,540 – $1,980 |
| 30x30 slab, 4 in (this page) | 12.22 | 734 | 550 | 12.25 cu yd | $3,670 – $5,138 | $1,715 – $2,205 |
| 24x40 slab, 4 in | 13.04 | 783 | 587 | 13.25 cu yd | $3,915 – $5,481 | $1,855 – $2,385 |
| 30x30 slab, 6 in | 18.33 | 1,100 | 825 | 18.5 cu yd | $5,500 – $7,700 | $2,590 – $3,330 |
Questions about a 30x30 slab, 4 in
How many bags of concrete for a 30x30 slab 4 inches thick?
Plan on 330 cubic feet for the 30x30, which is 550 80 lb bags, 734 60 lb bags, 880 50 lb or 1,100 40 lb bags once 10% waste is in.
How many yards of concrete for a 30x30 slab 4 inches thick?
12.22 cubic yards with waste (11.11 without) for a 30x30 at 4 in. Round the 30x30 order to 12.25 cu yd: plants batch in quarter yards and most won't send less than a yard.
How much does a 30x30 concrete slab 4 inches thick cost?
Concrete alone for the 30x30 runs about $1,715 – $2,205 for 12.25 cu yd of ready-mix delivered, or $3,670 – $5,138 for 734 60 lb bags. Add a 4 in gravel base and wire mesh and the bagged 30x30 plan comes to $4,542 – $6,557. Labor, forms and finishing for a 30x30 at 4 in come on top of these national ranges (as of 2026-09), which are not quotes.
How much does a 30x30 concrete slab 4 inches thick weigh?
About 49,500 lb (24.8 tons) of wet concrete for the 30x30, at 150 lb per cubic foot. The 550 80 lb bags for a 30x30 weigh 44,000 lb: about 30 trips in a pickup carrying 1,500 lb a load.
Where do control joints go on a 30x30 slab 4 inches thick?
On a 30x30 at 4 in, every 8 to 12 ft (24 to 36 times the thickness), sawn 1 in deep. On the 30x30 at 4 in, a joint every 10 ft or less means 2 joints each way: 9 panels of about 10 × 10 ft and 120 ft of saw cut.
Limitations
The 30x30 figures at 4 in are material estimates and typical price ranges, not a quote or a structural design. Confirm that 4 in, the reinforcement and the joint layout suit your soil, loads and local code for a 30x30 slab with a qualified professional.