12 by 12 ft slab at 8 inches
Calculate the specifications for a 12 ft by 12 ft residential slab at 8 inches thick with #4 bars at 18 inches apart. Excludes soil design considerations. Compliant with IRC R506.
Formula SSC-2026.1
Formula SSC-2026.1 · 4,000 PSI
Order volume
4.51 yd³
3.447 m³ placed+waste
Order weight
18,260 lb
8,283 kg
80 lb bags
203
5 pallets at 42 bags
60 lb bags
271
0.45 ft³ yield each
Rebar
312.00 ft
24 × 20 ft · 24 × 6 m · 229 lb
Ready-mix vs bags
$743.93
Truck $743.93 · 80 lb bags $1,370.25
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 | 4.10 yd³ | 10% | 4.51 yd³ / 3.447 m³ | USD | $743.93 | Source Spec Material / Tool |
| Short-load fee | Full load | — | 1 truck @ 10 yd³ | USD | $0.00 | Source Spec Material / Tool |
| 80 lb pre-mix bags | 184.4 bags | 10% | 203 bags | USD | $1,370.25 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 245.9 bags | 10% | 271 bags | USD | $1,463.40 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 24 sticks | 10% | 27 sticks / 24 × 6 m | USD | $378.00 | Source Spec Material / Tool |
| Rebar chairs | 81 crossings | 10% | 90 chairs | USD | $25.20 | Source Spec Material / Tool |
| Tie wire rolls | 81 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
$743.93
0.45 nominal 10 yd³ loads · 1 to order
80 lb bags
$1,370.25
60 lb alternative $1,463.40 · delivery weight 18,260 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 3.15 | 2.409 | 142 | 343 | $644.85 | $958.50 |
| 5 in | 3.49 | 2.668 | 158 | 343 | $700.87 | $1,066.50 |
| 6 in | 3.83 | 2.928 | 173 | 343 | $756.89 | $1,167.75 |
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 12 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 is designed to assist in determining the specifications for a residential concrete slab measuring 12 ft by 12 ft and 8 inches thick. The reinforcement consists of #4 bars placed 18 inches apart, ensuring structural integrity in accordance with IRC R506.
Please note that this tool does not include soil design considerations, which should be addressed separately by a qualified professional.
Code reference
IRC R506 - Concrete Floors on Ground
Field questions
- What is the thickness of the slab?
- The slab is designed to be 8 inches thick.
- What type of reinforcement is used?
- The slab uses #4 bars placed 18 inches apart.
- Is soil design included in this calculation?
- No, soil design considerations are excluded and should be evaluated separately.
- What code does this slab design comply with?
- This design complies with IRC R506 for concrete floors on ground.