An 8 × 8 slab at 4, 5 and 6 inches
Exact volume, the order rounded up to the next ¼ yd³ with 10% extra, and bags including the extra.
| Thickness | ft³ | Exact yd³ | Order yd³ | 80-lb bags | 60-lb bags | 50-lb bags | 40-lb bags |
|---|---|---|---|---|---|---|---|
| 4 in | 21.33 | 0.79 | 1 | 40 | 53 | 63 | 79 |
| 5 in | 26.67 | 0.99 | 1.25 | 49 | 66 | 79 | 98 |
| 6 in | 32 | 1.19 | 1.5 | 59 | 79 | 94 | 118 |
An 8 × 8 slab in metric
8 × 8 ft is about 2.44 m × 2.44 m, or 5.95 m². Here is the same slab at the common metric thicknesses, with 10% extra and the order rounded up to the next 0.1 m³.
| Thickness | Exact m³ | Order m³ | 30-kg bags | 25-kg bags | 20-kg bags |
|---|---|---|---|---|---|
| 100 mm | 0.595 | 0.7 | 47 | 57 | 73 |
| 125 mm | 0.743 | 0.9 | 58 | 71 | 91 |
| 150 mm | 0.892 | 1 | 70 | 85 | 110 |
Forms and a thickened edge
The edges of an 8 × 8 slab add up to 2 × (8 + 8) = 32 ft, so that's how many linear feet of form boards you need to go all the way around. The boards must be at least as tall as the slab is thick.
Many slabs are poured with a deeper edge around the outside. If yours has one, for example an edge 12 in deep and 12 in wide under a 4 in slab, the 8 × 8 needs 1.48 cubic yards instead of 0.79: 0.69 yd³ more. With 10% extra, order 1.75 yd³ or buy 74 80-lb bags. Use the slab calculator and choose "Slab with thickened edge" to enter your own edge size.
How an 8 × 8 compares
At 4 in thick, one cubic yard of concrete covers 81 ft². An 8 × 8 slab is 64 ft², so it needs less than one cubic yard (0.79 yd³).
- A 4 × 4 slab needs 0.2 yd³ (10 80-lb bags), which is 0.59 yd³ less than an 8 × 8.
- A 10 × 10 slab needs 1.23 yd³ (62 80-lb bags), which is 0.44 yd³ more than an 8 × 8.
Going from 4 in to 6 in thick adds 0.4 yd³ to an 8 × 8, or 19 more 80-lb bags, so settle the thickness before you order.
Bags or ready-mix for an 8 × 8?
At this size, bags are usually practical. If you'd rather order ready-mix, ask suppliers about minimum orders and small-load fees.
At 4 in, the 40 80-lb bags weigh 3,200 lb dry. At 6 in it's 59 bags. Ready-mix trucks carry 8 to 12 cubic yards (NRMCA), so an 8 × 8 needs one truck at 4 in. Enter your local prices in the calculator to compare costs.
Building codes set 3½ in as the minimum for slab-on-ground floors; the calculator warns you if you go thinner.
Other slab sizes
Questions people ask
How many yards of concrete for an 8 × 8 slab?
An 8 × 8 ft slab is 0.79 cubic yards at 4 in thick, 0.99 at 5 in and 1.19 at 6 in. With 10% extra, order 1, 1.25 or 1.5 cubic yards.
How many bags of concrete for an 8 × 8 slab?
At 4 in thick with 10% extra: 40 80-lb bags, 53 60-lb bags or 79 40-lb bags. At 6 in: 59 80-lb bags.
How much does an 8 × 8 slab weigh?
About 3,196 lb (1.6 tons) at 4 in thick, using 2,400 kg/m³ (about 150 lb/ft³).
How much concrete for an 8 × 8 slab in cubic meters?
8 × 8 ft is about 2.44 m × 2.44 m (5.95 m²). At 100 mm thick that's 0.595 m³; with 10% extra, order 0.7 m³ or buy 57 25-kg bags.
How many feet of form boards for an 8 × 8 slab?
The perimeter is 2 × (8 + 8) = 32 ft, so you need 32 linear feet of form boards around the edge, at least as tall as the slab is thick.
How many square feet is an 8 × 8 slab?
64 ft². At 4 in thick that's 21.33 ft³ of concrete, which is 0.79 cubic yards (cubic feet ÷ 27).
Related calculators
Sources
- QUIKRETE Concrete Mix No. 1101 product data sheet, retrieved October 2, 2026
- NRMCA, Concrete in Practice 31: Ordering Ready Mixed Concrete, retrieved October 2, 2026
- International Residential Code 2021, Section R506.1, retrieved October 2, 2026
- NRMCA, Concrete in Practice 36: Structural Lightweight Concrete, retrieved October 2, 2026
Last updated October 2, 2026. Read how we calculate, including formulas, waste defaults and rounding.