How much concrete for a 4 × 8 slab?
A 4 × 8 ft slab (32 sq ft) poured 4 inches thick takes 0.4 cubic yards of concrete. With 10% extra for uneven ground and spillage, order 0.43 cubic yards of ready-mix or buy 20 bags of 80 lb mix.
| Thickness | Exact volume | Order (+10%) | 80 lb bags | 60 lb bags | Typical use |
|---|---|---|---|---|---|
| 4 in | 0.4 yd³ | 0.43 yd³ (0.33 m³) | 20 | 27 | Patio, walkway, shed floor |
| 5 in | 0.49 yd³ | 0.54 yd³ (0.42 m³) | 25 | 33 | Hot tub pad, light driveway |
| 6 in | 0.59 yd³ | 0.65 yd³ (0.5 m³) | 30 | 40 | 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
11.7 cubic feet = 0.43 cubic yards = 0.33 m³. Above about 1 cubic yard, ready-mix delivery is usually cheaper and faster than bags.
Rough material cost (cheapest option)
$74Ready-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 4x8 slab?
At 4 inches thick, 20 bags of 80 lb concrete mix or 27 bags of 60 lb mix, including 10% extra. At 6 inches, 30 bags of 80 lb mix.
Should I use bags or ready-mix for a 4x8 slab?
Bags. At 0.43 cubic yards the job is small enough to mix by hand or with a rented mixer, and ready-mix suppliers charge a short-load fee for small orders.
How do you calculate concrete for a 4 by 8 slab?
Multiply length × width × thickness in feet: 4 × 8 × (4 ÷ 12) = 10.7 cubic feet. Divide by 27 to get 0.4 cubic yards, then add 5–10% extra.