12 by 18 ft slab at 4 inches
Calculate the specifications for a residential slab measuring 12 ft by 18 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
2.93 yd³
2.243 m³ placed+waste
Order weight
11,880 lb
5,389 kg
80 lb bags
132
4 pallets at 42 bags
60 lb bags
176
0.45 ft³ yield each
Rebar
318.00 ft
22 × 20 ft · 22 × 6 m · 234 lb
Ready-mix vs bags
$609.00
Truck $609.00 · 80 lb bags $891.00
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 | 2.67 yd³ | 10% | 2.93 yd³ / 2.243 m³ | USD | $484.00 | 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 | 120.0 bags | 10% | 132 bags | USD | $891.00 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 160.0 bags | 10% | 176 bags | USD | $950.40 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 22 sticks | 10% | 25 sticks / 22 × 6 m | USD | $350.00 | Source Spec Material / Tool |
| Rebar chairs | 117 crossings | 10% | 129 chairs | USD | $36.12 | Source Spec Material / Tool |
| Tie wire rolls | 117 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
$609.00
0.29 nominal 10 yd³ loads · 1 to order
80 lb bags
$891.00
60 lb alternative $950.40 · delivery weight 11,880 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 2.93 | 2.243 | 132 | 350 | $609.00 | $891.00 |
| 5 in | 3.67 | 2.803 | 165 | 350 | $730.00 | $1,113.75 |
| 6 in | 4.40 | 3.364 | 198 | 350 | $726.00 | $1,336.50 |
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.
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Project: 12 by 18 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 helps you determine the specifications for a residential slab, specifically designed to meet IRC R506 standards. The slab dimensions are 12 ft by 18 ft with a thickness of 4 inches, reinforced with #4 bars spaced 18 inches apart.
Please note that soil design considerations are not included in this calculation. It is essential to consult with a qualified engineer for a comprehensive assessment of soil conditions before proceeding with construction.
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 structural integrity.
- Why is soil design excluded from this calculator?
- Soil design is a complex aspect that depends on various factors such as soil type, load-bearing capacity, and moisture content. It is recommended to consult a qualified engineer for soil analysis.
- What does IRC R506 cover?
- IRC R506 outlines the requirements for concrete slabs, including thickness, reinforcement, and installation methods to ensure safety and durability.
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