8 by 30 ft slab at 6 inches
Calculate the design for an 8 ft by 30 ft residential slab at 6 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
6.36 yd³
4.859 m³ placed+waste
Order weight
25,740 lb
11,675 kg
80 lb bags
286
7 pallets at 42 bags
60 lb bags
382
0.45 ft³ yield each
Rebar
500.00 ft
41 × 20 ft · 41 × 6 m · 367 lb
Ready-mix vs bags
$1,048.67
Truck $1,048.67 · 80 lb bags $1,930.50
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 | 5.78 yd³ | 10% | 6.36 yd³ / 4.859 m³ | USD | $1,048.67 | 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 | 260.0 bags | 10% | 286 bags | USD | $1,930.50 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 346.7 bags | 10% | 382 bags | USD | $2,062.80 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 41 sticks | 10% | 46 sticks / 41 × 6 m | USD | $644.00 | Source Spec Material / Tool |
| Rebar chairs | 126 crossings | 10% | 139 chairs | USD | $38.92 | Source Spec Material / Tool |
| Tie wire rolls | 126 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
$1,048.67
0.64 nominal 10 yd³ loads · 1 to order
80 lb bags
$1,930.50
60 lb alternative $2,062.80 · delivery weight 25,740 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 5.21 | 3.987 | 235 | 550 | $860.44 | $1,586.25 |
| 5 in | 5.79 | 4.423 | 261 | 550 | $954.56 | $1,761.75 |
| 6 in | 6.36 | 4.859 | 286 | 550 | $1,048.67 | $1,930.50 |
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: 8 by 30 ft slab at 6 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
When designing a residential slab, it is crucial to consider the dimensions and reinforcement requirements. For a slab measuring 8 ft by 30 ft with a thickness of 6 inches, #4 rebar should be placed at 18-inch intervals to provide adequate support and structural integrity.
Note that soil design considerations are excluded from this calculation. Always consult a qualified engineer for specific site conditions and soil bearing capacity.
Code reference
IRC R506
Field questions
- What is the purpose of using #4 bars in the slab?
- Using #4 bars helps to reinforce the concrete slab, providing additional tensile strength and preventing cracking.
- Is soil design included in this slab calculation?
- No, soil design considerations are excluded. It is recommended to consult a qualified engineer for soil analysis.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete slabs, including reinforcement and thickness requirements.
Explore Related Engineering Calculations
- 14 by 12 ft slab at 8 inches
- 14 by 14 ft slab at 4 inches
- 8 by 8 ft slab at 8 inches
- 8 by 10 ft slab at 4 inches
- 14 by 14 ft slab at 5 inches
- 14 by 14 ft slab at 6 inches
- 50 Amp EV Charger Wire Size at 50, 75, and 100 Feet
- Deck Stair Stringer Calculator, 36 to 96 Inch Rise
- 6/12 Roof Pitch, Rafter Length, and Shingle Bundles
- 20 ft dry, US 48×40 pallets: Pallet Count, CBM, and Payload