18 by 12 ft slab at 4 inches
Calculate the specifications for a residential slab measuring 18 ft by 12 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.
Contractor sign-off
Project: 18 by 12 ft slab at 4 inches
Prepared by
Date
Verified by (PE / electrician / inspector)
License number
Signature
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 concrete slab measuring 18 ft by 12 ft with a thickness of 4 inches. The design incorporates #4 rebar placed at 18-inch intervals, ensuring structural integrity.
Note that soil design considerations are excluded from this calculation. For compliance, refer to the International Residential Code (IRC) Section R506, which outlines the requirements for concrete floors.
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 separate consideration that depends on local soil conditions and load-bearing capacities, which are not addressed in this calculator.
- What thickness is recommended for a residential slab?
- A thickness of 4 inches is commonly recommended for residential slabs, providing adequate support for typical loads.
Explore Related Engineering Calculations
- 14 by 12 ft slab at 8 inches
- 14 by 14 ft slab at 4 inches
- 8 by 8 ft slab at 8 inches
- 8 by 10 ft slab at 4 inches
- 14 by 14 ft slab at 5 inches
- 14 by 14 ft slab at 6 inches
- 50 Amp EV Charger Wire Size at 50, 75, and 100 Feet
- Deck Stair Stringer Calculator, 36 to 96 Inch Rise
- 6/12 Roof Pitch, Rafter Length, and Shingle Bundles
- 20 ft dry, US 48×40 pallets: Pallet Count, CBM, and Payload