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

Using #4 bars provides 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 site-specific and depends on various factors such as soil type, moisture content, and load-bearing capacity, which are not covered in this calculator.

What does IRC R506 cover?

IRC R506 covers the requirements for concrete floor slabs, including thickness, reinforcement, and placement, ensuring safety and durability in residential construction.

8 by 24 ft slab at 5 inches

Calculate the specifications for a residential slab measuring 8 ft by 24 ft at 5 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

3.26 yd³

2.492 m³ placed+waste

Order weight

13,200 lb

5,987 kg

80 lb bags

147

4 pallets at 42 bags

60 lb bags

196

0.45 ft³ yield each

Rebar

280.00 ft

29 × 20 ft · 29 × 6 m · 206 lb

Ready-mix vs bags

$662.78

Truck $662.78 · 80 lb bags $992.25

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	2.96 yd³	10%	3.26 yd³ / 2.492 m³	USD	$537.78	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	133.3 bags	10%	147 bags	USD	$992.25	Source Spec Material / Tool
60 lb pre-mix bags	177.8 bags	10%	196 bags	USD	$1,058.40	Source Spec Material / Tool
#4 rebar sticks, 20 ft	29 sticks	10%	32 sticks / 29 × 6 m	USD	$448.00	Source Spec Material / Tool
Rebar chairs	102 crossings	10%	113 chairs	USD	$31.64	Source Spec Material / Tool
Tie wire rolls	102 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

$662.78

0.33 nominal 10 yd³ loads · 1 to order

80 lb bags

$992.25

60 lb alternative $1,058.40 · delivery weight 13,200 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	2.61	1.994	118	308	$555.22	$796.50
5 in	3.26	2.492	147	308	$662.78	$992.25
6 in	3.91	2.990	176	308	$770.33	$1,188.00

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: 8 by 24 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 helps you determine the necessary specifications for a residential concrete slab measuring 8 ft by 24 ft with a thickness of 5 inches. The design incorporates #4 rebar placed at 18 inches on center, ensuring structural integrity.

Please note that soil design considerations are excluded from this calculation. Always consult a licensed engineer for site-specific soil conditions and compliance with local building codes.

Code reference

IRC R506

Field questions

What is the purpose of using #4 bars in the slab?: Using #4 bars provides 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 site-specific and depends on various factors such as soil type, moisture content, and load-bearing capacity, which are not covered in this calculator.
What does IRC R506 cover?: IRC R506 covers the requirements for concrete floor slabs, including thickness, reinforcement, and placement, ensuring safety and durability in residential construction.