20x20 Concrete Slab: Bags, Yards & Cost
A 20 × 20 ft slab (400 sq ft) 4 in thick is 133.3 cu ft, or 4.94 cu yd: 223 bags of 80 lb Quikrete Concrete Mix (234 with a 5% margin), 297 bags of 60 lb, or 145 bags of 80 lb Sakrete Maximizer. The 80 lb bags weigh 17,840 lb in total.
Your cost and bags vs a truck
Set up for: a 20 × 20 ft slab · Different project?
20x20 slab at 4, 5 and 6 inches
| Thickness | Cu yd | With 5% | 80 lb Quikrete | 60 lb Quikrete | 80 lb Maximizer | 80 lb 5000 Plus |
|---|---|---|---|---|---|---|
| 4 in | 4.94 | 5.19 | 223 | 297 | 145 | 223 |
| 5 in | 6.17 | 6.48 | 278 | 371 | 182 | 278 |
| 6 in | 7.41 | 7.78 | 334 | 445 | 218 | 334 |
Other sizes: 10x10 · 12x12 · 8x8 · 10x12 · 30x30 · 8x10 · 12x24 · 12x36 · 20x30 · 20x40
FAQ
How many bags of concrete for a 20x20 slab?
At 4 in thick: 223 bags of 80 lb Quikrete Concrete Mix or 297 of 60 lb (whole bags, no margin). At 6 in: 334 of 80 lb.
How many yards of concrete for a 20x20 slab?
4.94 cu yd at 4 in, 6.17 at 5 in and 7.41 at 6 in, before the 4–10% NRMCA suggests adding when you order.
How much does a 20x20 concrete slab cost?
We don't publish prices because they change by store and region. Multiply 223 bags by your store's 80 lb bag price, or 5.19 cu yd (4 in, with 5%) by your plant's price per yard plus delivery and short-load fees. Type those into the calculator to compare.
Sources
- Quikrete: QUIKRETE Concrete Mix (No. 1101) data sheet · fetched and reviewed 2026-11-10
- Quikrete: QUIKRETE online project calculator (calculator.js) · fetched and reviewed 2026-11-10
- Sakrete: Sakrete Maximizer Concrete Mix technical data sheet · fetched and reviewed 2026-11-10
- Sakrete: Sakrete 5000 Plus Concrete Mix technical data sheet · fetched and reviewed 2026-11-10
- NRMCA: CIP 31: Ordering Ready Mixed Concrete · fetched and reviewed 2026-11-10