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 improve overall structural integrity.

Why is soil design excluded from this calculation?

Soil design is site-specific and requires a geotechnical analysis to determine the appropriate soil bearing capacity and other factors that influence slab performance.

What thickness is standard for residential slabs?

The standard thickness for residential slabs typically ranges from 4 to 8 inches, depending on the load requirements and local building codes.

12 by 16 ft slab at 8 inches

Calculate the requirements for a residential slab measuring 12 ft by 16 ft 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

5.92 yd³

4.527 m³ placed+waste

Order weight

23,980 lb

10,877 kg

80 lb bags

267

7 pallets at 42 bags

60 lb bags

356

0.45 ft³ yield each

Rebar

388.00 ft

26 × 20 ft · 26 × 6 m · 285 lb

Ready-mix vs bags

$976.96

Truck $976.96 · 80 lb bags $1,802.25

Slab footprint and rebar gridLive scaled blueprint

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.

Bill of materials and shopping list
Item	Net	Waste	Order	Unit price	Line total	Source Spec Material / Tool
Ready-mix concrete	5.38 yd³	10%	5.92 yd³ / 4.527 m³	USD	$976.96	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	242.2 bags	10%	267 bags	USD	$1,802.25	Source Spec Material / Tool
60 lb pre-mix bags	323.0 bags	10%	356 bags	USD	$1,922.40	Source Spec Material / Tool
#4 rebar sticks, 20 ft	26 sticks	10%	29 sticks / 26 × 6 m	USD	$406.00	Source Spec Material / Tool
Rebar chairs	99 crossings	10%	109 chairs	USD	$30.52	Source Spec Material / Tool
Tie wire rolls	99 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

$976.96

0.59 nominal 10 yd³ loads · 1 to order

80 lb bags

$1,802.25

60 lb alternative $1,922.40 · delivery weight 23,980 lb

Side-by-side thickness comparison at the same footprint
Thickness	Order yd³	Order m³	80 lb bags	Rebar ft	Ready-mix	80 lb cost
4 in	4.02	3.073	181	427	$663.26	$1,221.75
5 in	4.50	3.437	203	427	$741.69	$1,370.25
6 in	4.97	3.800	224	427	$820.11	$1,512.00

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 16 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 preliminary design of a residential concrete slab measuring 12 ft by 16 ft and 8 inches thick, reinforced with #4 bars spaced at 18 inches. Please note that soil design considerations are excluded from this calculation.

For compliance, refer to the International Residential Code (IRC) Section R506, which outlines the requirements for concrete slabs, including reinforcement and thickness specifications.

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 improve overall structural integrity.
Why is soil design excluded from this calculation?: Soil design is site-specific and requires a geotechnical analysis to determine the appropriate soil bearing capacity and other factors that influence slab performance.
What thickness is standard for residential slabs?: The standard thickness for residential slabs typically ranges from 4 to 8 inches, depending on the load requirements and local building codes.