How much concrete for a 20 × 24 slab?
A 20 × 24 ft slab (480 sq ft) poured 4 inches thick takes 5.93 cubic yards of concrete. With 10% extra for uneven ground and spillage, order 6.52 cubic yards of ready-mix or buy 294 bags of 80 lb mix.
| Thickness | Exact volume | Order (+10%) | 80 lb bags | 60 lb bags | Typical use |
|---|---|---|---|---|---|
| 4 in | 5.93 yd³ | 6.52 yd³ (4.98 m³) | 294 | 392 | Patio, walkway, shed floor |
| 5 in | 7.41 yd³ | 8.15 yd³ (6.23 m³) | 367 | 489 | Hot tub pad, light driveway |
| 6 in | 8.89 yd³ | 9.78 yd³ (7.48 m³) | 440 | 587 | Driveway, garage floor |
Bag counts include the 10% extra and assume 0.60 ft³ per 80 lb bag and 0.45 ft³ per 60 lb bag.
Change the size, thickness or price
176 cubic feet = 6.52 cubic yards = 4.98 m³. Above about 1 cubic yard, ready-mix delivery is usually cheaper and faster than bags.
Rough material cost (cheapest option)
$1,108Ready-mix often has a short-load fee under 4–5 yd³. Rough 2026 US prices, edit to match local quotes.
FAQ
How many bags of concrete for a 20x24 slab?
At 4 inches thick, 294 bags of 80 lb concrete mix or 392 bags of 60 lb mix, including 10% extra. At 6 inches, 440 bags of 80 lb mix.
Should I use bags or ready-mix for a 20x24 slab?
Ready-mix is usually cheaper and much less work above about 1 cubic yard, and this slab needs 6.52. Under 4–5 yards many suppliers add a short-load fee, so compare a quote with 294 bags.
How do you calculate concrete for a 20 by 24 slab?
Multiply length × width × thickness in feet: 20 × 24 × (4 ÷ 12) = 160 cubic feet. Divide by 27 to get 5.93 cubic yards, then add 5–10% extra.