18 by 16 ft slab at 8 inches
Calculate the requirements for an 18 ft by 16 ft residential slab at 8 in thickness with #4 bars spaced at 18 in. Ensure compliance with IRC R506 guidelines.
Formula SSC-2026.1
Formula SSC-2026.1 · 4,000 PSI
Order volume
8.69 yd³
6.645 m³ placed+waste
Order weight
35,200 lb
15,966 kg
80 lb bags
392
10 pallets at 42 bags
60 lb bags
522
0.45 ft³ yield each
Rebar
542.00 ft
32 × 20 ft · 32 × 6 m · 398 lb
Ready-mix vs bags
$1,434.07
Truck $1,434.07 · 80 lb bags $2,646.00
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 | 7.90 yd³ | 10% | 8.69 yd³ / 6.645 m³ | USD | $1,434.07 | 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 | 355.6 bags | 10% | 392 bags | USD | $2,646.00 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 474.1 bags | 10% | 522 bags | USD | $2,818.80 | 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 |
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
$1,434.07
0.87 nominal 10 yd³ loads · 1 to order
80 lb bags
$2,646.00
60 lb alternative $2,818.80 · delivery weight 35,200 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 8 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 estimating the requirements for a residential slab measuring 18 ft by 16 ft with a thickness of 8 inches. The reinforcement specified is #4 bars placed 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 standards for concrete slabs in residential construction.
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 improving overall structural integrity.
- What thickness is recommended for a residential slab?
- For most residential applications, a thickness of 4 to 6 inches is common; however, in this case, an 8-inch thickness is specified for additional strength.
- Why is soil design excluded from this calculation?
- Soil design is a critical aspect that varies based on local conditions and requires specific geotechnical analysis, which is beyond the scope of this calculator.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete slabs, including requirements for thickness, reinforcement, and placement.