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How Much Concrete for a 12×24 Slab at 4 Inches?
A 12 ft × 24 ft slab 4 inches thick needs this much concrete — cubic yards and bag counts, calculated for you. Here is the answer, plus a calculator you can adjust if your measurements are slightly different.
Answer: 3.56 cubic yards
How it changes with thickness
Same area, different thickness:
| Thickness | 4 | 5 | 6 |
|---|---|---|---|
| Concrete needed | 3.56 cubic yards | 4.44 cubic yards | 5.33 cubic yards |
| 80 lb bags | 160 bags | 200 bags | 240 bags |
What a 12×24 slab at 4 inches actually involves
This is a truck pour. At 3.56 yd³ there is no realistic way to mix and place it by hand before the first batch starts to stiffen, so order ready-mix. Before you order, walk the route: a standard truck chute reaches roughly 16 to 18 ft from the truck, so the far corner needs to be inside that, or you will be running wheelbarrows from a heap.
The slab is 288 ft² and, at 4 inches thick, takes 96.00 ft³ of concrete — 3.56 yd³, weighing about 7.1 tons. Everything below is worked out from those figures.
Full material list
| Item | Quantity | Notes |
|---|---|---|
| Concrete | 3.56 yd³ | 160 × 80 lb bags, or 214 × 60 lb bags |
| Gravel base | 4.27 yd³ | order loose for 4 in compacted; see the gravel calculator |
| Form lumber | 79 lin ft | 2×4 or 2×6, includes 10% waste |
| Form stakes | 18 | roughly one every 4 ft of perimeter |
| Welded wire mesh | 7 sheets | 5×10 ft sheets of 6×6-W1.4 mesh, 10% overlap |
| Vapor barrier | 317 ft² | about 32 lin ft of 10 ft wide roll |
| Control joints | 3 joints | 48 lin ft of saw cut |
Control joints and cracking
Control joints stop a slab cracking wherever it likes. The conservative rule is to space them at twice the slab thickness in inches — here that means every 8 ft, which divides this slab into 2 × 3 panels of roughly 6.0 × 8.0 ft. That is 3 joints, about 48 linear ft of cutting. Get them in while the concrete is still green, typically 6 to 12 hours after finishing, before random cracks get there first.
Reinforcement at 4 inches
At 4 in, 7 sheets of 6×6-W1.4 welded wire mesh on chairs is the standard reinforcement. Lap the sheets about 6 in and keep them at mid-depth, so the steel ends up in the middle of the slab rather than resting on the sub-base. Mesh does not stop cracks forming — it holds them tight after they do, which is exactly what you want in a patio or shed floor. If this slab will take vehicles, step up to 5 or 6 in and use rebar instead.
Bagged concrete or a ready-mix truck?
| Option | Quantity | Estimated cost |
|---|---|---|
| Bagged 80 lb | 160 bags | $960 |
| Ready-mix delivered | 3.56 yd³ + short-load fee | $694 |
On these assumptions ready-mix is cheaper ($694 vs $960) as well as far less work. It only wins if the truck can actually reach the site and you can place the whole load without stopping. If access is a problem, bagged at $960 is the practical fallback and lets you pour in stages.
Costs assume $6 per 80 lb bag, $170 per cubic yard delivered, and a $90 short-load surcharge below 5 yd³. Ready-mix pricing moves with region, season and fuel, so treat these as a starting point for calling suppliers rather than a quote.
Pour day, in order
- Excavate to 8 in below finished grade: 4 in of slab plus 4 in of base.
- Compact the base in two lifts with a plate compactor, then damp it down so it does not pull water out of the mix.
- Set the forms to 4 in and check the level carefully. A truck load forgives nothing, and you cannot stop to fix it.
- Lay the vapor barrier, then the mesh on chairs at mid-depth.
- Confirm truck access and chute reach before you order. A standard chute covers roughly 16 to 18 ft, so walk the route and measure.
- Line up four or more people. Have boots, rakes, a screed board, a bull float and a hose waiting before the truck arrives.
- Place from the far corner back toward the truck, working continuously. Screed directly behind the placement, not after.
- Cut or tool the control joints while the concrete is still green, aiming for 6 to 12 hours after finishing. You need about 48 linear ft of cutting.
- Cover it and keep it damp for 7 days. Full design strength arrives at 28 days.
Local codes cover frost depth, reinforcement and permits, and they vary from place to place. Check with your local building department before you dig or pour.
Common questions
How many bags of concrete for a 12×24 slab at 4 inches?
160 bags of 80 lb mix, or 214 bags of 60 lb mix. A 12×24 slab at 4 in is 96.00 ft³, which is 3.56 yd³. An 80 lb bag yields about 0.60 ft³ and a 60 lb bag about 0.45 ft³, so divide the volume by the yield and round up.
How much does a 12×24 concrete slab cost?
Roughly $960 in 80 lb bags, or about $694 delivered as ready-mix, which includes a short-load surcharge because the order is under 5 cubic yards. Material only — it excludes excavation, base, reinforcement and labour.
How thick should a 12×24 slab be?
Four inches for a patio, shed floor or footpath. Five to six inches if vehicles will drive on it. This page is worked through at 4 inches, so switch the calculator above to compare thicknesses.
How much gravel goes under a 12×24 slab?
About 4.27 yd³ of loose crushed base for a 4 in compacted layer, covering 288 ft². Order it loose rather than already compacted — the material settles by roughly a fifth under a plate compactor.
Other sizes
- How Much Concrete for a 10×10 Slab at 4 Inches?
- How Much Concrete for a 10×10 Slab at 6 Inches?
- How Much Concrete for a 12×12 Slab at 4 Inches?
- How Much Concrete for a 12×12 Slab at 6 Inches?
- How Much Concrete for a 10×12 Slab at 4 Inches?
- How Much Concrete for a 10×12 Slab at 6 Inches?
- How Much Concrete for a 12×16 Slab at 4 Inches?
- How Much Concrete for a 12×16 Slab at 6 Inches?
- How Much Concrete for a 16×16 Slab at 4 Inches?
- How Much Concrete for a 16×16 Slab at 6 Inches?