How Many Bags of Concrete for a 20x20 Slab?
A 20x20 slab at 4" needs 245 bags of 80 lb concrete.
245bags
80 lb bags · estimated $1710.10 at $6.98/bag
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Estimated cost: ~$1710.10 (245 × $6.98/bag, Spring 2026 pricing)
Quick presets
Bag size
Material list
- 245 × 80 lb concrete mix bags — $1710.10 @ $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 | 245 | $6.98 | $1710.10 |
| 60 lb | 326 | $5.98 | $1949.48 |
| 40 lb | 489 | $4.98 | $2435.22 |
Prices are spring 2026 estimates. Above ~60 bags, price a ready-mix truck too — it is often cheaper.
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245 bags(80 lb)
$1710.10
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 slab?
A 20x20 slab at 4 inches needs about 245 bags of 80 lb or 326 bags of 60 lb concrete, including a 10% waste allowance.
How much does a 20x20 concrete slab cost?
About $1710 in 80 lb bags at current prices. Above ~60 bags, a ready-mix truck is often cheaper — the page shows both.
How many cubic feet of concrete is a 20x20 slab at 4 inches?
About 133.3 cubic feet, or 146.7 cubic feet once the 10% waste buffer is added.
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