12 by 8 ft slab at 5 inches
Calculate the specifications for a 12 ft by 8 ft residential slab with #4 bars at 18 in spacing. Ensure compliance with IRC R506. Soil design considerations are excluded.
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: 12 by 8 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 slab measuring 12 ft by 8 ft and 5 inches thick, reinforced with #4 bars spaced 18 inches apart. Please note that soil design is not included in this calculation.
For compliance with the International Residential Code (IRC) R506, ensure that your slab meets the necessary structural and material standards.
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 preventing cracking.
- Why is soil design excluded from this calculation?
- Soil design is a complex process that requires specific geotechnical analysis, which is not covered in this calculator.
- What thickness is recommended for residential slabs?
- A thickness of 5 inches is commonly recommended for residential slabs, but this can vary based on specific load requirements and local codes.