18 by 16 ft slab at 4 inches
Calculate the requirements for a residential slab measuring 18 ft by 16 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
406.00 ft
24 × 20 ft · 24 × 6 m · 298 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 | 24 sticks | 10% | 27 sticks / 24 × 6 m | USD | $378.00 | 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 |
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 | 447 | $770.33 | $1,188.00 |
| 5 in | 4.89 | 3.738 | 220 | 447 | $806.67 | $1,485.00 |
| 6 in | 5.87 | 4.485 | 264 | 447 | $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: 18 by 16 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 the preliminary design of a residential slab measuring 18 ft by 16 ft with a thickness of 4 inches. The slab incorporates #4 reinforcement bars spaced at 18 inches on center. Please 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 slabs in residential construction.
Code reference
IRC R506
Field questions
- What is the purpose of reinforcement bars in a concrete slab?
- Reinforcement bars, or rebar, are used in concrete slabs to enhance tensile strength and prevent cracking. They help distribute loads and improve the overall durability of the slab.
- Why is soil design excluded from this calculation?
- Soil design is excluded because it requires specific geotechnical analysis based on the site's soil conditions. This calculator focuses solely on the concrete slab dimensions and reinforcement.
- What does IRC R506 cover?
- IRC R506 covers the requirements for concrete floor slabs, including materials, thickness, reinforcement, and installation practices to ensure structural integrity in residential buildings.