8 by 12 ft slab at 5 inches
Calculate the specifications for a residential slab measuring 8 ft by 12 ft at 5 in thickness 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
1.63 yd³
1.246 m³ placed+waste
Order weight
6,600 lb
2,994 kg
80 lb bags
74
2 pallets at 42 bags
60 lb bags
98
0.45 ft³ yield each
Rebar
144.00 ft
15 × 20 ft · 15 × 6 m · 106 lb
Ready-mix vs bags
$393.89
Truck $393.89 · 80 lb bags $499.50
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 | 1.48 yd³ | 10% | 1.63 yd³ / 1.246 m³ | USD | $268.89 | 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 | 66.7 bags | 10% | 74 bags | USD | $499.50 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 88.9 bags | 10% | 98 bags | USD | $529.20 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 15 sticks | 10% | 17 sticks / 15 × 6 m | USD | $238.00 | 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
$393.89
0.16 nominal 10 yd³ loads · 1 to order
80 lb bags
$499.50
60 lb alternative $529.20 · delivery weight 6,600 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 1.30 | 0.997 | 59 | 158 | $340.11 | $398.25 |
| 5 in | 1.63 | 1.246 | 74 | 158 | $393.89 | $499.50 |
| 6 in | 1.96 | 1.495 | 88 | 158 | $447.67 | $594.00 |
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.
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Project: 8 by 12 ft slab at 5 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 helps you determine the requirements for a residential concrete slab measuring 8 ft by 12 ft and 5 inches thick. The design includes #4 rebar placed at 18 inches on center, which is crucial for structural integrity.
Please note that soil design considerations are excluded from this calculation. For accurate results, consult a professional engineer for site-specific soil conditions.
Code reference
IRC R506
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 overall strength.
- Why is soil design excluded from this calculation?
- Soil design is site-specific and requires a geotechnical analysis to determine the appropriate foundation design based on soil conditions.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete slabs on grade, ensuring they meet safety and performance standards.
- How thick should a residential slab be?
- The thickness of a residential slab can vary, but a common thickness is 4 to 6 inches, depending on the load and use of the slab.
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