12 by 30 ft slab at 4 inches
Calculate the requirements for a residential slab measuring 12 ft by 30 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
4.89 yd³
3.738 m³ placed+waste
Order weight
19,800 lb
8,981 kg
80 lb bags
220
6 pallets at 42 bags
60 lb bags
294
0.45 ft³ yield each
Rebar
522.00 ft
39 × 20 ft · 39 × 6 m · 384 lb
Ready-mix vs bags
$806.67
Truck $806.67 · 80 lb bags $1,485.00
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 | 4.44 yd³ | 10% | 4.89 yd³ / 3.738 m³ | USD | $806.67 | 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 | 200.0 bags | 10% | 220 bags | USD | $1,485.00 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 266.7 bags | 10% | 294 bags | USD | $1,587.60 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 39 sticks | 10% | 43 sticks / 39 × 6 m | USD | $602.00 | Source Spec Material / Tool |
| Rebar chairs | 189 crossings | 10% | 208 chairs | USD | $58.24 | Source Spec Material / Tool |
| Tie wire rolls | 189 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
$806.67
0.49 nominal 10 yd³ loads · 1 to order
80 lb bags
$1,485.00
60 lb alternative $1,587.60 · delivery weight 19,800 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 4.89 | 3.738 | 220 | 574 | $806.67 | $1,485.00 |
| 5 in | 6.11 | 4.672 | 275 | 574 | $1,008.33 | $1,856.25 |
| 6 in | 7.33 | 5.607 | 330 | 574 | $1,210.00 | $2,227.50 |
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 30 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 assists in determining the specifications for a residential concrete slab measuring 12 ft by 30 ft with a thickness of 4 inches. The design incorporates #4 rebar placed at 18-inch intervals, which is essential for structural integrity.
Please note that soil design considerations are excluded from this calculation. For accurate results, consult a qualified engineer for site-specific soil conditions and compliance with IRC R506.
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 prevent cracking and improve load-bearing capacity.
- 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 the ground, including thickness, reinforcement, and placement.
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