How Much Concrete for a 30 × 30 Slab?
A 30 × 30 ft slab is 900 sq ft. It needs 12.22 cubic yards of concrete at 4 inches thick or 18.33 yd³ at 6 inches, including 10% extra.
| Order | 4 in thick | 6 in thick |
|---|---|---|
| Cubic yards | 12.22 | 18.33 |
| 80-lb bags | 550 | 825 |
| 60-lb bags | 734 | 1,100 |
| 50-lb bags | 880 | 1,320 |
| 40-lb bags | 1,100 | 1,650 |
| Cubic meters | 9.34 | 14.02 |
Concrete needed
12.22 cubic yards
330.0 ft³ · 9.34 m³ · includes 10% extra
You need about 12.22 cubic yards of concrete, or 550 bags of 80 lb mix.
Bags of premix
- 1,10040 lb bags
- 88050 lb bags
- 73460 lb bags
- 55080 lb bags
- —20 kg bags
- —25 kg bags
- Before extra11.11 yd³ (300.0 ft³)
- Weight of bags44,000 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 12.22 yd³, bags are not realistic (550 × 80 lb). This is a ready-mix pour, often with a contractor's crew and sometimes a pump.
Estimate only, not a quote or engineering advice. Disclaimer
A 30 × 30 ft slab suits a three-car garage or a large shop.
30 × 30 slab at other thicknesses
| Thickness | yd³ exact | yd³ +10% | 80-lb bags | 60-lb bags |
|---|---|---|---|---|
| 3.5 in | 9.72 | 10.69 | 482 | 642 |
| 4 in | 11.11 | 12.22 | 550 | 734 |
| 5 in | 13.89 | 15.28 | 688 | 917 |
| 6 in | 16.67 | 18.33 | 825 | 1,100 |
| 8 in | 22.22 | 24.44 | 1,100 | 1,467 |
How it's worked out
For bags, the 330.0 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 42,000 lb, using the 140 lb/ft³ unit weight QUIKRETE lists for its Concrete Mix.
Bags or a truck?
At 12.22 yd³, bags are not realistic: it would take 550 × 80-lb bags. This is a ready-mix pour, and at this size often a job for a concrete contractor with a crew, and sometimes a pump.
For a slab this size, the number to give a ready-mix supplier is the yardage: 12.22 yd³ at 4 inches or 18.33 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 30x30 slab?
11.11 cubic yards at 4 inches thick and 16.67 yd³ at 6 inches, before waste. With 10% extra, order 12.22 or 18.33 yd³.
How many bags of concrete for a 30x30 slab?
At 4 inches with 10% extra: 550 bags of 80-lb mix, 734 of 60 lb, 880 of 50 lb or 1,100 of 40 lb. At 6 inches: 825 bags of 80 lb or 1,100 of 60 lb.
How many cubic feet of concrete for a 30x30 slab?
300.0 ft³ at 4 inches (900 sq ft × 4 ÷ 12) and 450.0 ft³ at 6 inches, before waste.
How thick should a 30x30 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)