12 by 8 ft slab at 8 inches
Calculate the specifications for a residential slab measuring 12 ft by 8 ft at 8 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
3.10 yd³
2.367 m³ placed+waste
Order weight
12,540 lb
5,688 kg
80 lb bags
140
4 pallets at 42 bags
60 lb bags
186
0.45 ft³ yield each
Rebar
224.00 ft
19 × 20 ft · 21 × 6 m · 165 lb
Ready-mix vs bags
$635.89
Truck $635.89 · 80 lb bags $945.00
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 | 2.81 yd³ | 10% | 3.10 yd³ / 2.367 m³ | USD | $510.89 | 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 | 126.7 bags | 10% | 140 bags | USD | $945.00 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 168.9 bags | 10% | 186 bags | USD | $1,004.40 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 19 sticks | 10% | 21 sticks / 21 × 6 m | USD | $294.00 | Source Spec Material / Tool |
| Rebar chairs | 54 crossings | 10% | 60 chairs | USD | $16.80 | Source Spec Material / Tool |
| Tie wire rolls | 54 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
$635.89
0.31 nominal 10 yd³ loads · 1 to order
80 lb bags
$945.00
60 lb alternative $1,004.40 · delivery weight 12,540 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 2.28 | 1.744 | 103 | 246 | $501.44 | $695.25 |
| 5 in | 2.49 | 1.900 | 112 | 246 | $535.06 | $756.00 |
| 6 in | 2.69 | 2.056 | 121 | 246 | $568.67 | $816.75 |
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: 12 by 8 ft slab at 8 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 assists in determining the requirements for a residential concrete slab measuring 12 feet by 8 feet with a thickness of 8 inches. The slab is reinforced with #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 consult a qualified engineer for soil analysis and site-specific conditions.
Code reference
IRC R506 - Concrete Floors on Ground
Field questions
- What is the purpose of using #4 bars in the slab?
- The #4 bars provide reinforcement to the concrete slab, helping to control cracking and improve load-bearing capacity.
- Why is soil design excluded from this calculation?
- Soil design is excluded because it requires site-specific analysis and should be performed by a qualified engineer to ensure proper foundation support.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete floors on the ground, including reinforcement requirements and thickness specifications.
- What are the dimensions of the slab in this calculation?
- The slab dimensions are 12 feet in length and 8 feet in width, with a thickness of 8 inches.