18 by 24 ft slab at 8 inches
Calculate the specifications for an 18 ft by 24 ft residential slab at 8 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
12.82 yd³
9.801 m³ placed+waste
Order weight
51,920 lb
23,551 kg
80 lb bags
577
14 pallets at 42 bags
60 lb bags
770
0.45 ft³ yield each
Rebar
786.00 ft
53 × 20 ft · 53 × 6 m · 578 lb
Ready-mix vs bags
$2,115.26
Truck $2,115.26 · 80 lb bags $3,894.75
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 | 11.65 yd³ | 10% | 12.82 yd³ / 9.801 m³ | USD | $2,115.26 | Source Spec Material / Tool |
| Short-load fee | Full load | — | 2 truck @ 10 yd³ | USD | $0.00 | Source Spec Material / Tool |
| 80 lb pre-mix bags | 524.4 bags | 10% | 577 bags | USD | $3,894.75 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 699.3 bags | 10% | 770 bags | USD | $4,158.00 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 53 sticks | 10% | 59 sticks / 53 × 6 m | USD | $826.00 | Source Spec Material / Tool |
| Rebar chairs | 221 crossings | 10% | 244 chairs | USD | $68.32 | Source Spec Material / Tool |
| Tie wire rolls | 221 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
$2,115.26
1.28 nominal 10 yd³ loads · 2 to order
80 lb bags
$3,894.75
60 lb alternative $4,158.00 · delivery weight 51,920 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 8.04 | 6.147 | 362 | 865 | $1,326.52 | $2,443.50 |
| 5 in | 9.23 | 7.060 | 416 | 865 | $1,523.70 | $2,808.00 |
| 6 in | 10.43 | 7.974 | 470 | 865 | $1,720.89 | $3,172.50 |
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 24 ft slab at 8 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 is designed to assist in determining the specifications for a residential slab measuring 18 ft by 24 ft with a thickness of 8 inches. The slab incorporates #4 rebar bars spaced at 18 inches, ensuring structural integrity.
Please note that soil design considerations are excluded from this calculation. For accurate results, consult a qualified engineer for soil analysis and site-specific conditions.
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, enhancing its tensile strength and helping to prevent cracking.
- Why is soil design excluded from this calculation?
- Soil design is a critical factor that varies by location and requires site-specific analysis. This calculator focuses solely on the slab dimensions and reinforcement.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete slabs on grade, ensuring they meet safety and performance standards.