18 by 18 ft slab at 6 inches
Calculate the requirements for a residential slab measuring 18 ft by 18 ft at 6 in thick with #4 bars spaced at 18 in. Refer to IRC R506 for guidelines.
Formula SSC-2026.1
Formula SSC-2026.1 · 4,000 PSI
Order volume
7.99 yd³
6.105 m³ placed+waste
Order weight
32,340 lb
14,669 kg
80 lb bags
360
9 pallets at 42 bags
60 lb bags
480
0.45 ft³ yield each
Rebar
612.00 ft
34 × 20 ft · 34 × 6 m · 450 lb
Ready-mix vs bags
$1,317.56
Truck $1,317.56 · 80 lb bags $2,430.00
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 | 7.26 yd³ | 10% | 7.99 yd³ / 6.105 m³ | USD | $1,317.56 | 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 | 326.7 bags | 10% | 360 bags | USD | $2,430.00 | Source Spec Material / Tool |
| 60 lb pre-mix bags | 435.6 bags | 10% | 480 bags | USD | $2,592.00 | Source Spec Material / Tool |
| #4 rebar sticks, 20 ft | 34 sticks | 10% | 38 sticks / 34 × 6 m | USD | $532.00 | Source Spec Material / Tool |
| Rebar chairs | 169 crossings | 10% | 186 chairs | USD | $52.08 | Source Spec Material / Tool |
| Tie wire rolls | 169 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
$1,317.56
0.80 nominal 10 yd³ loads · 1 to order
80 lb bags
$2,430.00
60 lb alternative $2,592.00 · delivery weight 32,340 lb
| Thickness | Order yd³ | Order m³ | 80 lb bags | Rebar ft | Ready-mix | 80 lb cost |
|---|---|---|---|---|---|---|
| 4 in | 6.25 | 4.776 | 282 | 673 | $1,030.74 | $1,903.50 |
| 5 in | 7.12 | 5.441 | 321 | 673 | $1,174.15 | $2,166.75 |
| 6 in | 7.99 | 6.105 | 360 | 673 | $1,317.56 | $2,430.00 |
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 18 ft slab at 6 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 preliminary design of a residential slab measuring 18 ft by 18 ft with a thickness of 6 inches. The slab incorporates #4 reinforcement bars spaced at 18 inches on center. Please note that soil design considerations are excluded from this calculation.
For compliance with the International Residential Code (IRC), refer to Section R506, which outlines the requirements for concrete floors, including reinforcement and thickness specifications.
Code reference
IRC R506
Field questions
- What is the thickness of the slab?
- The slab is designed to be 6 inches thick.
- What type of reinforcement is used?
- The slab uses #4 bars spaced 18 inches apart.
- Is soil design included in this calculation?
- No, soil design considerations are excluded from this calculation.
- Where can I find more information on code compliance?
- Refer to IRC R506 for guidelines on concrete floor requirements.