8 by 30 ft slab at 8 inches
Calculate the specifications for an 8 ft by 30 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
7.50 yd³
5.731 m³ placed+waste
Order weight
30,360 lb
13,771 kg
80 lb bags
338
9 pallets at 42 bags
60 lb bags
450
0.45 ft³ yield each
Rebar
500.00 ft
41 × 20 ft · 41 × 6 m · 367 lb
Ready-mix vs bags
$1,236.89
Truck $1,236.89 · 80 lb bags $2,281.50
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 | 6.81 yd³ | 10% | 7.50 yd³ / 5.731 m³ | USD | $1,236.89 | 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 | 306.7 bags | 10% | 338 bags | USD | $2,281.50 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 408.9 bags | 10% | 450 bags | USD | $2,430.00 | 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
$1,236.89
0.75 nominal 10 yd³ loads · 1 to order
80 lb bags
$2,281.50
60 lb alternative $2,430.00 · delivery weight 30,360 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 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 the design of a residential concrete slab measuring 8 ft by 30 ft with a thickness of 8 inches. Reinforcement is provided using #4 bars spaced at 18 inches apart, which is essential for maintaining structural integrity.
Please note that soil design considerations are excluded from this calculation. It is important to consult a qualified engineer for soil analysis and other site-specific conditions.
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 resist cracking and improve overall durability.
- Why is soil design excluded from this calculator?
- Soil design is site-specific and requires a thorough analysis by a qualified engineer to ensure proper load-bearing capacity and stability.
- What does IRC R506 cover?
- IRC R506 provides guidelines for the design and construction of concrete slabs on grade, including reinforcement requirements and curing practices.
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