8 by 24 ft slab at 4 inches
Calculate the specifications for an 8 ft by 24 ft residential slab with #4 bars at 18 in spacing. Ensure compliance with IRC R506 while excluding soil design considerations.
Formula SSC-2026.1
Formula SSC-2026.1 · 4,000 PSI
Order volume
2.61 yd³
1.994 m³ placed+waste
Order weight
10,560 lb
4,790 kg
80 lb bags
118
3 pallets at 42 bags
60 lb bags
157
0.45 ft³ yield each
Rebar
280.00 ft
29 × 20 ft · 29 × 6 m · 206 lb
Ready-mix vs bags
$555.22
Truck $555.22 · 80 lb bags $796.50
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 | 2.37 yd³ | 10% | 2.61 yd³ / 1.994 m³ | USD | $430.22 | 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 | 106.7 bags | 10% | 118 bags | USD | $796.50 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 142.2 bags | 10% | 157 bags | USD | $847.80 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 29 sticks | 10% | 32 sticks / 29 × 6 m | USD | $448.00 | Source Spec Material / Tool |
| Rebar chairs | 102 crossings | 10% | 113 chairs | USD | $31.64 | Source Spec Material / Tool |
| Tie wire rolls | 102 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
$555.22
0.26 nominal 10 yd³ loads · 1 to order
80 lb bags
$796.50
60 lb alternative $847.80 · delivery weight 10,560 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 2.61 | 1.994 | 118 | 308 | $555.22 | $796.50 |
| 5 in | 3.26 | 2.492 | 147 | 308 | $662.78 | $992.25 |
| 6 in | 3.91 | 2.990 | 176 | 308 | $770.33 | $1,188.00 |
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 24 ft slab at 4 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 design of a residential slab measuring 8 ft by 24 ft with a thickness of 4 inches. The use of #4 rebar at 18-inch spacing is included in the calculations. Please note that soil design considerations are excluded from this calculator.
For compliance with the International Residential Code (IRC) R506, ensure that all local building codes and regulations are followed when constructing your slab.
Code reference
IRC R506
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 calculator?
- Soil design is a complex aspect that depends on various factors such as soil type, load-bearing capacity, and local conditions, which are beyond the scope of this calculator.
- What thickness is recommended for a residential slab?
- A thickness of 4 inches is commonly recommended for residential slabs, but this may vary based on specific project requirements and local codes.
- How do I ensure compliance with IRC R506?
- To ensure compliance with IRC R506, follow the guidelines provided in the code regarding slab thickness, reinforcement, and other construction practices.