18 by 10 ft slab at 5 inches
Calculate the specifications for a residential slab measuring 18 ft by 10 ft at 5 in thickness with #4 bars at 18 in spacing. Ensure compliance with IRC R506 guidelines.
Formula SSC-2026.1
Formula SSC-2026.1 · 4,000 PSI
Order volume
3.06 yd³
2.336 m³ placed+waste
Order weight
12,375 lb
5,613 kg
80 lb bags
138
4 pallets at 42 bags
60 lb bags
184
0.45 ft³ yield each
Rebar
256.00 ft
20 × 20 ft · 20 × 6 m · 188 lb
Ready-mix vs bags
$629.17
Truck $629.17 · 80 lb bags $931.50
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 | 2.78 yd³ | 10% | 3.06 yd³ / 2.336 m³ | USD | $504.17 | 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 | 125.0 bags | 10% | 138 bags | USD | $931.50 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 166.7 bags | 10% | 184 bags | USD | $993.60 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 20 sticks | 10% | 22 sticks / 20 × 6 m | USD | $308.00 | Source Spec Material / Tool |
| Rebar chairs | 91 crossings | 10% | 101 chairs | USD | $28.28 | Source Spec Material / Tool |
| Tie wire rolls | 91 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
$629.17
0.31 nominal 10 yd³ loads · 1 to order
80 lb bags
$931.50
60 lb alternative $993.60 · delivery weight 12,375 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 2.44 | 1.869 | 110 | 282 | $528.33 | $742.50 |
| 5 in | 3.06 | 2.336 | 138 | 282 | $629.17 | $931.50 |
| 6 in | 3.67 | 2.803 | 165 | 282 | $730.00 | $1,113.75 |
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 10 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
This calculator helps you determine the requirements for a residential slab measuring 18 ft by 10 ft with a thickness of 5 inches. The design includes #4 reinforcement bars spaced at 18 inches on center. Please note that soil design considerations are excluded from this calculation.
Ensure that your slab design complies with the International Residential Code (IRC) Section R506 for concrete slabs on grade.
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 prevent cracking and ensuring structural integrity.
- Why is soil design excluded from this calculation?
- Soil design is site-specific and requires a geotechnical evaluation to determine the appropriate soil bearing capacity and other factors that affect slab performance.
- What does IRC R506 cover?
- IRC R506 outlines the requirements for concrete slabs on grade, including thickness, reinforcement, and placement to ensure durability and safety.
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