How Much Concrete for a 12 × 24 Slab?
A 12 × 24 ft slab is 288 sq ft. It needs 3.91 cubic yards of concrete at 4 inches thick or 5.87 yd³ at 6 inches, including 10% extra.
| Order | 4 in thick | 6 in thick |
|---|---|---|
| Cubic yards | 3.91 | 5.87 |
| 80-lb bags | 176 | 264 |
| 60-lb bags | 235 | 352 |
| 50-lb bags | 282 | 423 |
| 40-lb bags | 352 | 528 |
| Cubic meters | 2.99 | 4.49 |
Concrete needed
3.91 cubic yards
105.6 ft³ · 2.99 m³ · includes 10% extra
You need about 3.91 cubic yards of concrete, or 176 bags of 80 lb mix.
Bags of premix
- 35240 lb bags
- 28250 lb bags
- 23560 lb bags
- 17680 lb bags
- —20 kg bags
- —25 kg bags
- Before extra3.56 yd³ (96.0 ft³)
- Weight of bags14,080 lb
- Per hole—
- Ready-mix costAdd a price per yd³
- Bagged costAdd a price per bag
One 80 lb bag makes about 0.60 ft³ (manufacturer's published yield). Bags are rounded up.
At 3.91 yd³ that is 176 × 80 lb bags (14,080 lb) to mix. Most people order ready-mix at this size; ask suppliers for their minimum load and any short-load fee.
Estimate only, not a quote or engineering advice. Disclaimer
A 12 × 24 ft slab is a typical single-car parking pad, carport or workshop shed base.
12 × 24 slab at other thicknesses
| Thickness | yd³ exact | yd³ +10% | 80-lb bags | 60-lb bags |
|---|---|---|---|---|
| 3.5 in | 3.11 | 3.42 | 154 | 206 |
| 4 in | 3.56 | 3.91 | 176 | 235 |
| 5 in | 4.44 | 4.89 | 220 | 294 |
| 6 in | 5.33 | 5.87 | 264 | 352 |
| 8 in | 7.11 | 7.82 | 352 | 470 |
How it's worked out
For bags, the 105.6 ft³ (with extra) is divided by each bag's yield: 0.60 ft³ for 80 lb, 0.45 for 60 lb, 0.375 for 50 lb and 0.30 for 40 lb, then rounded up. At 4 inches the slab itself weighs about 13,400 lb, using the 140 lb/ft³ unit weight QUIKRETE lists for its Concrete Mix.
Bags or a truck?
At 3.91 yd³ you would need 176 × 80-lb bags (about 14,080 lb) and a long session with a mixer and helpers. Most people order ready-mix at this size: call suppliers with the yardage and ask for their minimum load and any short-load fee.
For a slab this size, the number to give a ready-mix supplier is the yardage: 3.91 yd³ at 4 inches or 5.87 yd³ at 6 inches, with 10% extra already included. Some people order a little less than the full allowance and keep a few bags on hand to top off.
Don't forget the base: most slabs sit on a compacted layer of gravel, and thicker edges or footings around the perimeter add concrete. Use the footing calculator for a thickened edge.
Frequently asked questions
How many yards of concrete for a 12x24 slab?
3.56 cubic yards at 4 inches thick and 5.33 yd³ at 6 inches, before waste. With 10% extra, order 3.91 or 5.87 yd³.
How many bags of concrete for a 12x24 slab?
At 4 inches with 10% extra: 176 bags of 80-lb mix, 235 of 60 lb, 282 of 50 lb or 352 of 40 lb. At 6 inches: 264 bags of 80 lb or 352 of 60 lb.
How many cubic feet of concrete for a 12x24 slab?
96.0 ft³ at 4 inches (288 sq ft × 4 ÷ 12) and 144.0 ft³ at 6 inches, before waste.
How thick should a 12x24 slab be?
Four inches is usual for patios, walkways and shed pads. Garage floors, driveways and pads for heavy loads are commonly 5 to 6 inches. Follow local code or your plans for anything structural.
Other slab sizes
Related
Sources
- QUIKRETE: Concrete Mix No. 1101 data sheet (Revised Oct 2022; checked Nov 11, 2026)