What is the purpose of using #4 bars in the slab?

The #4 bars provide reinforcement to the concrete slab, helping to control cracking and improve load-bearing capacity.

Why is soil design excluded from this calculation?

Soil design is a complex aspect that varies by location and requires specific analysis. This calculator focuses solely on the slab dimensions and reinforcement.

What thickness is recommended for a residential slab?

A thickness of 6 inches is commonly recommended for residential slabs to ensure adequate strength and durability.

How do I ensure compliance with IRC R506?

To ensure compliance, follow the guidelines outlined in IRC R506 regarding slab thickness, reinforcement, and placement.

16 by 18 ft slab at 6 inches

Calculate the specifications for a residential slab measuring 16 ft by 18 ft with a thickness of 6 inches and #4 rebar at 18-inch spacing. Note: Soil design is excluded. Refer to IRC R506 for guidelines.

Formula SSC-2026.1

Formula SSC-2026.1 · 4,000 PSI

Order volume

7.17 yd³

5.482 m³ placed+waste

Order weight

29,040 lb

13,172 kg

80 lb bags

323

8 pallets at 42 bags

60 lb bags

431

0.45 ft³ yield each

Rebar

542.00 ft

32 × 20 ft · 32 × 6 m · 398 lb

Ready-mix vs bags

$1,183.11

Truck $1,183.11 · 80 lb bags $2,180.25

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	6.52 yd³	10%	7.17 yd³ / 5.482 m³	USD	$1,183.11	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	293.3 bags	10%	323 bags	USD	$2,180.25	Source Spec Material / Tool
60 lb pre-mix bags	391.1 bags	10%	431 bags	USD	$2,327.40	Source Spec Material / Tool
#4 rebar sticks, 20 ft	32 sticks	10%	36 sticks / 32 × 6 m	USD	$504.00	Source Spec Material / Tool
Rebar chairs	143 crossings	10%	158 chairs	USD	$44.24	Source Spec Material / Tool
Tie wire rolls	143 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

$1,183.11

0.72 nominal 10 yd³ loads · 1 to order

80 lb bags

$2,180.25

60 lb alternative $2,327.40 · delivery weight 29,040 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	5.65	4.319	255	596	$932.15	$1,721.25
5 in	6.41	4.901	289	596	$1,057.63	$1,950.75
6 in	7.17	5.482	323	596	$1,183.11	$2,180.25

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: 16 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 assists in determining the requirements for a residential concrete slab measuring 16 feet by 18 feet with a thickness of 6 inches. The design incorporates #4 reinforcing bars placed at 18-inch intervals to enhance structural integrity.

It is important to note that soil design considerations are excluded from this calculation. For comprehensive guidelines on slab construction, refer to the International Residential Code (IRC) section R506.

Code reference

IRC R506

Field questions

What is the purpose of using #4 bars in the slab?: The #4 bars provide reinforcement to the concrete slab, helping to control cracking and improve load-bearing capacity.
Why is soil design excluded from this calculation?: Soil design is a complex aspect that varies by location and requires specific analysis. This calculator focuses solely on the slab dimensions and reinforcement.
What thickness is recommended for a residential slab?: A thickness of 6 inches is commonly recommended for residential slabs to ensure adequate strength and durability.
How do I ensure compliance with IRC R506?: To ensure compliance, follow the guidelines outlined in IRC R506 regarding slab thickness, reinforcement, and placement.