12 by 24 ft slab at 4 inches
Calculate the requirements for a residential slab measuring 12 ft by 24 ft at 4 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
3.91 yd³
2.990 m³ placed+waste
Order weight
15,840 lb
7,185 kg
80 lb bags
176
5 pallets at 42 bags
60 lb bags
235
0.45 ft³ yield each
Rebar
420.00 ft
35 × 20 ft · 35 × 6 m · 309 lb
Ready-mix vs bags
$770.33
Truck $770.33 · 80 lb bags $1,188.00
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 | 3.56 yd³ | 10% | 3.91 yd³ / 2.990 m³ | USD | $645.33 | 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 | 160.0 bags | 10% | 176 bags | USD | $1,188.00 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 213.3 bags | 10% | 235 bags | USD | $1,269.00 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 35 sticks | 10% | 39 sticks / 35 × 6 m | USD | $546.00 | Source Spec Material / Tool |
| Rebar chairs | 153 crossings | 10% | 169 chairs | USD | $47.32 | Source Spec Material / Tool |
| Tie wire rolls | 153 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
$770.33
0.39 nominal 10 yd³ loads · 1 to order
80 lb bags
$1,188.00
60 lb alternative $1,269.00 · delivery weight 15,840 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 3.91 | 2.990 | 176 | 462 | $770.33 | $1,188.00 |
| 5 in | 4.89 | 3.738 | 220 | 462 | $806.67 | $1,485.00 |
| 6 in | 5.87 | 4.485 | 264 | 462 | $968.00 | $1,782.00 |
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: 12 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 determining the specifications for a residential slab measuring 12 ft by 24 ft with a thickness of 4 inches. The slab incorporates #4 rebar at 18-inch spacing, which is essential for structural integrity.
It is important to note that soil design considerations are excluded from this calculation. For accurate results, consult with a qualified engineer regarding soil conditions and other site-specific factors.
Code reference
IRC R506 - Concrete Floors on Ground
Field questions
- What is the purpose of using #4 bars in the slab?
- The #4 bars are used to reinforce the concrete slab, providing additional strength and helping to control cracking.
- Why is soil design excluded from this calculation?
- Soil design is site-specific and requires a detailed analysis of the soil conditions, which is beyond the scope of this calculator.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete floors on ground, including thickness, reinforcement, and placement.