40x40 Concrete Slab, 4 Inches Thick
Poured 4 in thick, a 40 × 40 ft slab covering 1,600 sq ft needs about 21.73 cubic yards of concrete once 10% is added for waste. For ready-mix, order 21.75 cu yd for the 40x40, about $3,045 – $3,915 delivered. Bagged, the same 40x40 is 978 80 lb or 1,304 60 lb bags, about $6,520 – $9,128 for the concrete alone.
- Ready-mix order
- 21.75 cu yd
- Ready-mix cost
- $3,045 – $3,915
- 80 lb bags
- 978
- Bag cost
- $6,520 – $9,128
Materials only for a 40x40 at 4 in, from national price ranges as of 2026-09; not a live quote.
Planning a 40x40 slab
A 40x40 slab is a four-car garage, a big square shop with a center work area, or a machine shed with doors on two sides.
At 1,600 sq ft, the pour is big enough that most owners hire a concrete contractor with a laser screed or a full crew.
A square plan like this is joint-friendly: at 4 in, panels of about 10 ft square divide the floor into a neat grid.
Before you pour the 40x40 at 4 in
- Get the doors and any interior walls on the plan before the joint layout is set.
- If equipment will be heavy, consider 5 or 6 in for the whole slab or just the drive lanes.
- Book a pump if the truck cannot reach the middle of the slab.
Full plan for a 40x40 slab, 4 in
- Area
- 1,600 sq ft
- Thickness
- 4 in
- Volume
- 21.73 cu yd
Bagged concrete estimate (DIY)
$8,069 – $11,651
Est. as of 2026-09 — not a live quote
Ready-mix delivered (materials only)
$3,045 – $3,915
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 1,956 × 40 lb, 1,565 × 50 lb or 978 × 80 lb bags. 1,304 bags
- Ready-mix concrete Alternative to bagged mix; most suppliers have a 1 cu yd order minimum. 21.75 cu yd
- Compactable gravel sub-base 4 in compacted base beneath the slab. 26.67 tons
- 6x6 welded wire mesh Reinforcement for crack control; not a substitute for engineered rebar on structural slabs. 1,760 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: 88,000 lb (44 tons).
- Prices are national-average retail/delivery ranges as of 2026-09, not live quotes.
Bags or ready-mix for a 40x40 slab, 4 in?
The 40x40 at 4 in needs 3 trucks: 21.75 cu yd at 8 cu yd a load, the low end of what a truck carries, for about $3,045 – $3,915. 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 1,600 sq ft at 4 in, and ask about a pump if the truck can't reach every corner of the 40x40. On the 40x40, ready-mix comes out cheaper by about $4,344 at the middle of each range, and it saves mixing 978 bags.
Is 4 in thick enough for a 40x40 slab?
Many residential garage floors the size of this 40x40 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 40x40 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 40x40 takes about 32.59 cu yd.
Control joints for a 40x40 slab at 4 in
Like any slab, a 4 in 40x40 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 40x40 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 40x40 at 4 in, a joint every 10 ft or less means 3 joints each way: 16 panels of about 10 × 10 ft and 240 ft of saw cut.
How much a 40x40 slab 4 in thick weighs
At roughly 150 lb per cubic foot of wet concrete, a 40x40 at 4 in puts about 88,000 lb (44 tons) on the ground. As bags, the 40x40 is 978 80 lb bags, 78,240 lb in all: about 53 trips in a pickup carrying 1,500 lb a load. Nobody hauls 78,240 lb of bags for a 40x40 in a pickup; it comes by ready-mix truck or as pallets on a delivery truck.
The 40x40 at 4 in against nearby sizes
Every row uses the same 10% waste and prices as the 40x40 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 |
|---|---|---|---|---|---|---|
| 30x50 slab, 4 in | 20.37 | 1,223 | 917 | 20.5 cu yd | $6,115 – $8,561 | $2,870 – $3,690 |
| 40x40 slab, 4 in (this page) | 21.73 | 1,304 | 978 | 21.75 cu yd | $6,520 – $9,128 | $3,045 – $3,915 |
| 30x60 slab, 4 in | 24.44 | 1,467 | 1,100 | 24.5 cu yd | $7,335 – $10,269 | $3,430 – $4,410 |
Questions about a 40x40 slab, 4 in
How many bags of concrete for a 40x40 slab 4 inches thick?
A 40x40 slab at 4 in takes about 978 80 lb bags or 1,304 60 lb bags (or 1,565 50 lb, 1,956 40 lb), with 10% added for waste: 586.7 cubic feet in all.
How many yards of concrete for a 40x40 slab 4 inches thick?
The 40x40 measures out at 19.75 cubic yards, or 21.73 with 10% for waste. Order 21.75 cu yd for the 40x40, since ready-mix is sold in quarter yards with a 1 yard minimum at most plants.
How much does a 40x40 concrete slab 4 inches thick cost?
Concrete alone for the 40x40 runs about $3,045 – $3,915 for 21.75 cu yd of ready-mix delivered, or $6,520 – $9,128 for 1,304 60 lb bags. Add a 4 in gravel base and wire mesh and the bagged 40x40 plan comes to $8,069 – $11,651. Labor, forms and finishing for a 40x40 at 4 in come on top of these national ranges (as of 2026-09), which are not quotes.
How much does a 40x40 concrete slab 4 inches thick weigh?
About 88,000 lb (44 tons) of wet concrete for the 40x40, at 150 lb per cubic foot. The 978 80 lb bags for a 40x40 weigh 78,240 lb: about 53 trips in a pickup carrying 1,500 lb a load.
Where do control joints go on a 40x40 slab 4 inches thick?
On a 40x40 at 4 in, every 8 to 12 ft (24 to 36 times the thickness), sawn 1 in deep. On the 40x40 at 4 in, a joint every 10 ft or less means 3 joints each way: 16 panels of about 10 × 10 ft and 240 ft of saw cut.
Limitations
The 40x40 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 40x40 slab with a qualified professional.