18 by 16 ft slab at 6 inches
Calculate the specifications for a residential slab measuring 18 ft by 16 ft at 6 in thick 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
7.17 yd³
5.482 m³ placed+waste
Order weight
29,040 lb
13,172 kg
80 lb bags
323
8 pallets at 42 bags
60 lb bags
431
0.45 ft³ yield each
Rebar
542.00 ft
32 × 20 ft · 32 × 6 m · 398 lb
Ready-mix vs bags
$1,183.11
Truck $1,183.11 · 80 lb bags $2,180.25
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 | 6.52 yd³ | 10% | 7.17 yd³ / 5.482 m³ | USD | $1,183.11 | 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 | 293.3 bags | 10% | 323 bags | USD | $2,180.25 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 391.1 bags | 10% | 431 bags | USD | $2,327.40 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 32 sticks | 10% | 36 sticks / 32 × 6 m | USD | $504.00 | Source Spec Material / Tool |
| Rebar chairs | 143 crossings | 10% | 158 chairs | USD | $44.24 | Source Spec Material / Tool |
| Tie wire rolls | 143 ties | 10% | 1 rolls | USD | $8.00 | Source Spec Material / Tool |
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Ready-mix truck
$1,183.11
0.72 nominal 10 yd³ loads · 1 to order
80 lb bags
$2,180.25
60 lb alternative $2,327.40 · delivery weight 29,040 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 5.65 | 4.319 | 255 | 596 | $932.15 | $1,721.25 |
| 5 in | 6.41 | 4.901 | 289 | 596 | $1,057.63 | $1,950.75 |
| 6 in | 7.17 | 5.482 | 323 | 596 | $1,183.11 | $2,180.25 |
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 16 ft slab at 6 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 18 ft by 16 ft and 6 inches thick. The use of #4 rebar at 18-inch spacing is included in the design. Please note that soil design considerations are excluded from this calculation.
For compliance with the International Residential Code (IRC) R506, proper attention to reinforcement and slab thickness is essential to ensure structural integrity.
Code reference
IRC R506
Field questions
- What is the purpose of using #4 bars in the slab?
- The #4 bars provide tensile strength to the concrete slab, helping to prevent cracking and ensuring durability under load.
- Why is soil design excluded from this calculation?
- Soil design is a separate consideration that involves evaluating the bearing capacity and stability of the soil beneath the slab, which is not covered in this calculator.
- What thickness is recommended for a residential slab?
- A thickness of 6 inches is commonly recommended for residential slabs to provide adequate strength and support for typical loads.