How much concrete for a 30 × 40 slab?
A 30 × 40 ft slab (1,200 sq ft) poured 4 inches thick takes 14.81 cubic yards of concrete. With 10% extra for uneven ground and spillage, order 16.3 cubic yards of ready-mix or buy 734 bags of 80 lb mix.
| Thickness | Exact volume | Order (+10%) | 80 lb bags | 60 lb bags | Typical use |
|---|---|---|---|---|---|
| 4 in | 14.81 yd³ | 16.3 yd³ (12.46 m³) | 734 | 978 | Patio, walkway, shed floor |
| 5 in | 18.52 yd³ | 20.37 yd³ (15.57 m³) | 917 | 1223 | Hot tub pad, light driveway |
| 6 in | 22.22 yd³ | 24.44 yd³ (18.69 m³) | 1100 | 1467 | 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
440 cubic feet = 16.3 cubic yards = 12.46 m³. Above about 1 cubic yard, ready-mix delivery is usually cheaper and faster than bags.
Rough material cost (cheapest option)
$2,770Ready-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 30x40 slab?
At 4 inches thick, 734 bags of 80 lb concrete mix or 978 bags of 60 lb mix, including 10% extra. At 6 inches, 1100 bags of 80 lb mix.
Should I use bags or ready-mix for a 30x40 slab?
Ready-mix is usually cheaper and much less work above about 1 cubic yard, and this slab needs 16.3. Under 4–5 yards many suppliers add a short-load fee, so compare a quote with 734 bags.
How do you calculate concrete for a 30 by 40 slab?
Multiply length × width × thickness in feet: 30 × 40 × (4 ÷ 12) = 400 cubic feet. Divide by 27 to get 14.81 cubic yards, then add 5–10% extra.