How Many Bags of Concrete for a 20x20 Slab at 6 Inches?
A 20x20 slab at 6" needs 367 bags of 80 lb concrete.
80 lb bags · estimated $2561.66 at $6.98/bag
Estimated cost: ~$2561.66 (367 × $6.98/bag, Spring 2026 pricing)
Quick presets
Material list
- 367 × 80 lb concrete mix bags — $2561.66 @ $6.98/bag (Spring 2026)Home Depot ↗Lowe's ↗
- Wheelbarrow or mixing tub
- Mixing hoe or drill paddle
- Margin trowel or float
Multi-bag comparison
| Bag size | Bags | Price/bag | Total |
|---|---|---|---|
| 80 lbBest value | 367 | $6.98 | $2561.66 |
| 60 lb | 489 | $5.98 | $2924.22 |
| 40 lb | 734 | $4.98 | $3655.32 |
Prices are spring 2026 estimates. Above ~60 bags, price a ready-mix truck too — it is often cheaper.
How this is calculated
We convert your dimensions to cubic feet, add a 10% waste buffer for spillage and an uneven subgrade, then divide by the bag's yield and round up to the next full bag.
FAQ
How many bags of concrete for a 20x20 driveway at 6 inches?
A 20x20 slab at 6 inches needs about 367 bags of 80 lb or 489 bags of 60 lb concrete, including 10% waste.
Is 6 inches thick enough for a driveway?
Yes. 6 inches is the standard thickness for residential driveways and areas that carry vehicle weight; 4 inches is only for patios and walkways.
Should I use bags or a ready-mix truck for a 20x20 driveway?
At 367 bags this is a large pour. A ready-mix truck is usually cheaper and faster above ~60 bags — the page shows both options side by side.