8 by 8 ft slab at 6 inches
Calculate the requirements for an 8 ft by 8 ft residential slab at 6 in depth with #4 bars at 18 in spacing. Ensure compliance with IRC R506 standards.
Formula SSC-2026.1
Formula SSC-2026.1 · 4,000 PSI
Order volume
1.87 yd³
1.433 m³ placed+waste
Order weight
7,590 lb
3,443 kg
80 lb bags
85
3 pallets at 42 bags
60 lb bags
113
0.45 ft³ yield each
Rebar
160.00 ft
16 × 20 ft · 16 × 6 m · 118 lb
Ready-mix vs bags
$434.22
Truck $434.22 · 80 lb bags $573.75
Grid lines are equalized so the drawing stays readable. The order count uses on-center spacing with a bar at each end of the layout, then holds concrete cover in the field.
| Item | Net | Waste | Order | Unit price | Line total | Source Spec Material / Tool |
|---|---|---|---|---|---|---|
| Ready-mix concrete | 1.70 yd³ | 10% | 1.87 yd³ / 1.433 m³ | USD | $309.22 | Source Spec Material / Tool |
| Short-load fee | Under 4 yd³ | — | 1 truck @ 10 yd³ | USD | $125.00 | Source Spec Material / Tool |
| 80 lb pre-mix bags | 76.7 bags | 10% | 85 bags | USD | $573.75 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 102.2 bags | 10% | 113 bags | USD | $610.20 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 16 sticks | 10% | 18 sticks / 16 × 6 m | USD | $252.00 | Source Spec Material / Tool |
| Rebar chairs | 36 crossings | 10% | 40 chairs | USD | $11.20 | Source Spec Material / Tool |
| Tie wire rolls | 36 ties | 10% | 1 rolls | USD | $8.00 | Source Spec Material / Tool |
Source links open a product search on the Amazon storefront for the selected currency. SiteSpecCalc may earn a commission. The link does not change the quantities above.
Ready-mix truck
$434.22
0.19 nominal 10 yd³ loads · 1 to order
80 lb bags
$573.75
60 lb alternative $610.20 · delivery weight 7,590 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 1.63 | 1.246 | 74 | 176 | $393.89 | $499.50 |
| 5 in | 1.75 | 1.339 | 79 | 176 | $414.06 | $533.25 |
| 6 in | 1.87 | 1.433 | 85 | 176 | $434.22 | $573.75 |
Show the deterministic formula
Slab ft³ = L × W × thickness ÷ 12. Thickened-edge extra = footing band × (footing depth − slab thickness), with corner squares counted once.
yd³ = ft³ ÷ 27. m³ = ft³ × 0.0283168. Weight uses 150 lb/ft³, then the header converts that pound total at 1 lb = 0.45359237 kg. 80 lb bags yield 0.6 ft³ and 60 lb bags yield 0.45 ft³. Currency changes the price labels only.
Bars across a span = floor(span ÷ spacing) + 1. Order sticks = that count, plus 10, 5, or 15 percent waste, cut from 20 ft and 6 m stock. Chairs = one per grid intersection.
Contractor sign-off
Project: 8 by 8 ft slab at 6 inches
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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.
Engineering notes
This calculator is designed to assist in the planning of a residential slab measuring 8 ft by 8 ft and 6 inches in thickness. The slab incorporates #4 rebar spaced at 18 inches on center, adhering to the guidelines set forth in IRC R506.
Please note that soil design considerations are excluded from this calculation. It is essential to evaluate the soil conditions separately to ensure proper support for the slab.
Code reference
IRC R506 - Concrete Floors on Ground
Field questions
- What is the purpose of using #4 bars in the slab?
- Using #4 bars helps to reinforce the concrete slab, providing additional tensile strength and reducing the risk of cracking.
- Why is soil design excluded from this calculation?
- Soil design is a separate consideration that depends on various factors such as soil type, load-bearing capacity, and moisture content, which are not addressed in this calculator.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete floors on the ground, including reinforcement requirements and installation practices.