30x30 Concrete Slab, 6 Inches Thick
Poured 6 in thick, a 30 × 30 ft slab covering 900 sq ft needs about 18.33 cubic yards of concrete once 10% is added for waste. For ready-mix, order 18.5 cu yd for the 30x30, about $2,590 – $3,330 delivered. Bagged, the same 30x30 is 825 80 lb or 1,100 60 lb bags, about $5,500 – $7,700 for the concrete alone.
- Ready-mix order
- 18.5 cu yd
- Ready-mix cost
- $2,590 – $3,330
- 80 lb bags
- 825
- Bag cost
- $5,500 – $7,700
Materials only for a 30x30 at 6 in, from national price ranges as of 2026-09; not a live quote.
Why pour a 30x30 slab 6 inches thick
A 6 in 30x30 suits a shop that will hold a car lift, a tractor with a loader, or a work truck, or a building on soft or clay soil.
At 6 in, the joint spacing opens up to roughly 12 to 18 ft, so a 30x30 can be cut into four 15 ft panels, and many builders reinforce it with rebar on chairs.
The pour more than doubles a single truck, so this is a planned delivery of several loads with a crew sized for it, and often a pump.
Before you pour the 30x30 at 6 in
- Read the lift maker's slab requirements and mark where its posts will stand.
- Order rebar and chairs early; the rebar calculator gives you a grid for this size.
- Book the pump and the trucks together so they arrive on the same schedule.
Full plan for a 30x30 slab, 6 in
- Area
- 900 sq ft
- Thickness
- 6 in
- Volume
- 18.33 cu yd
Bagged concrete estimate (DIY)
$6,372 – $9,119
Est. as of 2026-09 — not a live quote
Ready-mix delivered (materials only)
$2,590 – $3,330
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 1,650 × 40 lb, 1,320 × 50 lb or 825 × 80 lb bags. 1,100 bags
- Ready-mix concrete Alternative to bagged mix; most suppliers have a 1 cu yd order minimum. 18.5 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: 74,250 lb (37.1 tons).
- Prices are national-average retail/delivery ranges as of 2026-09, not live quotes.
Bags or ready-mix for a 30x30 slab, 6 in?
The 30x30 at 6 in needs 3 trucks: 18.5 cu yd at 8 cu yd a load, the low end of what a truck carries, for about $2,590 – $3,330. 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 6 in, and ask about a pump if the truck can't reach every corner of the 30x30. On the 30x30, ready-mix comes out cheaper by about $3,640 at the middle of each range, and it saves mixing 825 bags.
Is 6 in thick enough for a 30x30 slab?
6 in is the step up for a 30x30 that will carry heavy pickups, a loaded trailer or a car lift, or that sits on soft or clay soil. Check your local code and the equipment maker's slab specs; at 4 in the same 30x30 would take about 12.22 cu yd. For a 30x30 at 6 in, many builders use rebar rather than wire mesh; the rebar calculator sizes a grid for it. See also: 30x30 slab at 4 in.
Control joints for a 30x30 slab at 6 in
A 30x30 slab at 6 in shrinks as it cures, and without joints it cracks wherever it chooses. The usual rule (ACI and PCA guidance) puts joints in a 30x30 at 6 in every 12 to 18 ft, 24 to 36 times the thickness, cut 1.5 in deep (a quarter of the thickness) as soon as the surface takes the saw without raveling, usually within the first day.
On the 30x30 at 6 in, a joint every 15 ft or less means 1 joint each way: 4 panels of about 15 × 15 ft and 60 ft of saw cut.
How much a 30x30 slab 6 in thick weighs
At roughly 150 lb per cubic foot of wet concrete, a 30x30 at 6 in puts about 74,250 lb (37.1 tons) on the ground. As bags, the 30x30 is 825 80 lb bags, 66,000 lb in all: about 44 trips in a pickup carrying 1,500 lb a load. Nobody hauls 66,000 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 6 in against nearby sizes
Every row uses the same 10% waste and prices as the 30x30 at 6 in; costs are for the concrete only.
| Slab | Cu yd | 60 lb bags | 80 lb bags | Ready-mix order | Bags cost | Ready-mix cost |
|---|---|---|---|---|---|---|
| 20x20 slab, 6 in | 8.15 | 489 | 367 | 8.25 cu yd | $2,445 – $3,423 | $1,215 – $1,595 |
| 30x30 slab, 6 in (this page) | 18.33 | 1,100 | 825 | 18.5 cu yd | $5,500 – $7,700 | $2,590 – $3,330 |
| 30x30 slab, 4 in | 12.22 | 734 | 550 | 12.25 cu yd | $3,670 – $5,138 | $1,715 – $2,205 |
Questions about a 30x30 slab, 6 in
How many bags of concrete for a 30x30 slab 6 inches thick?
A 30x30 slab at 6 in takes about 825 80 lb bags or 1,100 60 lb bags (or 1,320 50 lb, 1,650 40 lb), with 10% added for waste: 495 cubic feet in all.
How many yards of concrete for a 30x30 slab 6 inches thick?
The 30x30 measures out at 16.67 cubic yards, or 18.33 with 10% for waste. Order 18.5 cu yd for the 30x30, since ready-mix is sold in quarter yards with a 1 yard minimum at most plants.
How much does a 30x30 concrete slab 6 inches thick cost?
Concrete alone for the 30x30 runs about $2,590 – $3,330 for 18.5 cu yd of ready-mix delivered, or $5,500 – $7,700 for 1,100 60 lb bags. Add a 4 in gravel base and wire mesh and the bagged 30x30 plan comes to $6,372 – $9,119. Labor, forms and finishing for a 30x30 at 6 in come on top of these national ranges (as of 2026-09), which are not quotes.
How much does a 30x30 concrete slab 6 inches thick weigh?
About 74,250 lb (37.1 tons) of wet concrete for the 30x30, at 150 lb per cubic foot. The 825 80 lb bags for a 30x30 weigh 66,000 lb: about 44 trips in a pickup carrying 1,500 lb a load.
Where do control joints go on a 30x30 slab 6 inches thick?
On a 30x30 at 6 in, every 12 to 18 ft (24 to 36 times the thickness), sawn 1.5 in deep. On the 30x30 at 6 in, a joint every 15 ft or less means 1 joint each way: 4 panels of about 15 × 15 ft and 60 ft of saw cut.
Limitations
The 30x30 figures at 6 in are material estimates and typical price ranges, not a quote or a structural design. Confirm that 6 in, the reinforcement and the joint layout suit your soil, loads and local code for a 30x30 slab with a qualified professional.