How Much Concrete for a 30 × 50 Slab?
A 30 × 50 ft slab is 1,500 sq ft. It needs 20.37 cubic yards of concrete at 4 inches thick or 30.56 yd³ at 6 inches, including 10% extra.
| Order | 4 in thick | 6 in thick |
|---|---|---|
| Cubic yards | 20.37 | 30.56 |
| 80-lb bags | 917 | 1,375 |
| 60-lb bags | 1,223 | 1,834 |
| 50-lb bags | 1,467 | 2,200 |
| 40-lb bags | 1,834 | 2,750 |
| Cubic meters | 15.57 | 23.36 |
Concrete needed
20.37 cubic yards
550.0 ft³ · 15.57 m³ · includes 10% extra
You need about 20.37 cubic yards of concrete, or 917 bags of 80 lb mix.
Bags of premix
- 1,83440 lb bags
- 1,46750 lb bags
- 1,22360 lb bags
- 91780 lb bags
- —20 kg bags
- —25 kg bags
- Before extra18.52 yd³ (500.0 ft³)
- Weight of bags73,360 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 20.37 yd³, bags are not realistic (917 × 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 × 50 ft slab is a big shop or barn floor. Large slabs are usually poured with control joints planned in advance and often in sections.
30 × 50 slab at other thicknesses
| Thickness | yd³ exact | yd³ +10% | 80-lb bags | 60-lb bags |
|---|---|---|---|---|
| 3.5 in | 16.20 | 17.82 | 803 | 1,070 |
| 4 in | 18.52 | 20.37 | 917 | 1,223 |
| 5 in | 23.15 | 25.46 | 1,146 | 1,528 |
| 6 in | 27.78 | 30.56 | 1,375 | 1,834 |
| 8 in | 37.04 | 40.74 | 1,834 | 2,445 |
How it's worked out
For bags, the 550.0 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 70,000 lb, using the 140 lb/ft³ unit weight QUIKRETE lists for its Concrete Mix.
Bags or a truck?
At 20.37 yd³, bags are not realistic: it would take 917 × 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: 20.37 yd³ at 4 inches or 30.56 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 30x50 slab?
18.52 cubic yards at 4 inches thick and 27.78 yd³ at 6 inches, before waste. With 10% extra, order 20.37 or 30.56 yd³.
How many bags of concrete for a 30x50 slab?
At 4 inches with 10% extra: 917 bags of 80-lb mix, 1,223 of 60 lb, 1,467 of 50 lb or 1,834 of 40 lb. At 6 inches: 1,375 bags of 80 lb or 1,834 of 60 lb.
How many cubic feet of concrete for a 30x50 slab?
500.0 ft³ at 4 inches (1,500 sq ft × 4 ÷ 12) and 750.0 ft³ at 6 inches, before waste.
How thick should a 30x50 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)