12 by 12 ft slab at 5 inches
Calculate the requirements for a 12 ft x 12 ft residential slab with #4 bars at 18 in spacing. Ensure compliance with IRC R506 standards. Soil design considerations are excluded.
Formula SSC-2026.1
Formula SSC-2026.1 · 4,000 PSI
Order volume
2.44 yd³
1.869 m³ placed+waste
Order weight
9,900 lb
4,491 kg
80 lb bags
110
3 pallets at 42 bags
60 lb bags
147
0.45 ft³ yield each
Rebar
216.00 ft
18 × 20 ft · 18 × 6 m · 159 lb
Ready-mix vs bags
$528.33
Truck $528.33 · 80 lb bags $742.50
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 | 2.22 yd³ | 10% | 2.44 yd³ / 1.869 m³ | USD | $403.33 | Source Spec Material / Tool |
| Short-load fee | Under 4 yd³ | — | 1 truck @ 10 yd³ | USD | $125.00 | Source Spec Material / Tool |
| 80 lb pre-mix bags | 100.0 bags | 10% | 110 bags | USD | $742.50 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 133.3 bags | 10% | 147 bags | USD | $793.80 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 18 sticks | 10% | 20 sticks / 18 × 6 m | USD | $280.00 | Source Spec Material / Tool |
| Rebar chairs | 81 crossings | 10% | 90 chairs | USD | $25.20 | Source Spec Material / Tool |
| Tie wire rolls | 81 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
$528.33
0.24 nominal 10 yd³ loads · 1 to order
80 lb bags
$742.50
60 lb alternative $793.80 · delivery weight 9,900 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 1.96 | 1.495 | 88 | 238 | $447.67 | $594.00 |
| 5 in | 2.44 | 1.869 | 110 | 238 | $528.33 | $742.50 |
| 6 in | 2.93 | 2.243 | 132 | 238 | $609.00 | $891.00 |
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: 12 by 12 ft slab at 5 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 assists in determining the structural requirements for a residential slab measuring 12 ft by 12 ft with a thickness of 5 inches, reinforced with #4 bars spaced at 18 inches. Compliance with the International Residential Code (IRC) R506 is essential for ensuring safety and durability.
Please note that soil design considerations are excluded from this calculation. It is recommended to consult a qualified engineer for soil analysis and foundation design.
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 structural integrity.
- Why is soil design excluded from this calculation?
- Soil design is a critical aspect that varies based on site-specific conditions. It is recommended to consult a geotechnical engineer for proper soil analysis.
- What does IRC R506 cover?
- IRC R506 outlines the requirements for concrete floors and slabs, including design, reinforcement, and construction practices to ensure safety and compliance.