18 by 24 ft slab at 5 inches
Calculate the requirements for a residential slab measuring 18 ft by 24 ft at 5 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
7.33 yd³
5.607 m³ placed+waste
Order weight
29,700 lb
13,472 kg
80 lb bags
330
8 pallets at 42 bags
60 lb bags
440
0.45 ft³ yield each
Rebar
618.00 ft
43 × 20 ft · 43 × 6 m · 454 lb
Ready-mix vs bags
$1,210.00
Truck $1,210.00 · 80 lb bags $2,227.50
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 | 6.67 yd³ | 10% | 7.33 yd³ / 5.607 m³ | USD | $1,210.00 | 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 | 300.0 bags | 10% | 330 bags | USD | $2,227.50 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 400.0 bags | 10% | 440 bags | USD | $2,376.00 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 43 sticks | 10% | 48 sticks / 43 × 6 m | USD | $672.00 | 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
$1,210.00
0.73 nominal 10 yd³ loads · 1 to order
80 lb bags
$2,227.50
60 lb alternative $2,376.00 · delivery weight 29,700 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 5.87 | 4.485 | 264 | 680 | $968.00 | $1,782.00 |
| 5 in | 7.33 | 5.607 | 330 | 680 | $1,210.00 | $2,227.50 |
| 6 in | 8.80 | 6.728 | 396 | 680 | $1,452.00 | $2,673.00 |
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 24 ft slab at 5 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
When designing a residential slab, it's crucial to consider the dimensions and reinforcement requirements. This slab measures 18 ft by 24 ft with a thickness of 5 inches, utilizing #4 rebar spaced at 18 inches on center. Compliance with IRC R506 ensures that your slab meets the necessary structural integrity standards.
Please note that soil design considerations are excluded from this calculation and should be addressed separately based on 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, helping to control cracking and improve overall structural integrity.
- Why is soil design excluded from this calculation?
- Soil design is site-specific and depends on various factors such as soil type, moisture content, and load-bearing capacity, which are not covered in this general slab design.
- 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.
- How do I ensure my slab is compliant with IRC R506?
- To ensure compliance, follow the specifications outlined in IRC R506 regarding dimensions, reinforcement, and curing practices during construction.