What is the purpose of using rebar in a concrete slab?

Rebar provides tensile strength to the concrete, helping to prevent cracking and improve the overall durability of the slab.

Why is soil design excluded from this calculator?

Soil design is site-specific and requires a thorough analysis by a qualified engineer to ensure proper load-bearing capacity and stability.

What does IRC R506 cover?

IRC R506 provides guidelines for the design and construction of concrete slabs on grade, including specifications for materials, reinforcement, and placement.

14 by 30 ft slab at 5 inches

Calculate the specifications for a residential slab measuring 14 ft by 30 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

7.13 yd³

5.451 m³ placed+waste

Order weight

28,875 lb

13,097 kg

80 lb bags

321

8 pallets at 42 bags

60 lb bags

428

0.45 ft³ yield each

Rebar

594.00 ft

41 × 20 ft · 41 × 6 m · 436 lb

Ready-mix vs bags

$1,176.39

Truck $1,176.39 · 80 lb bags $2,166.75

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	6.48 yd³	10%	7.13 yd³ / 5.451 m³	USD	$1,176.39	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	291.7 bags	10%	321 bags	USD	$2,166.75	Source Spec Material / Tool
60 lb pre-mix bags	388.9 bags	10%	428 bags	USD	$2,311.20	Source Spec Material / Tool
#4 rebar sticks, 20 ft	41 sticks	10%	46 sticks / 41 × 6 m	USD	$644.00	Source Spec Material / Tool
Rebar chairs	210 crossings	10%	231 chairs	USD	$64.68	Source Spec Material / Tool
Tie wire rolls	210 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

$1,176.39

0.71 nominal 10 yd³ loads · 1 to order

80 lb bags

$2,166.75

60 lb alternative $2,311.20 · delivery weight 28,875 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	5.70	4.361	257	653	$941.11	$1,734.75
5 in	7.13	5.451	321	653	$1,176.39	$2,166.75
6 in	8.56	6.541	385	653	$1,411.67	$2,598.75

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: 14 by 30 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 is designed to assist in determining the specifications for a residential concrete slab measuring 14 ft by 30 ft with a thickness of 5 inches. The slab incorporates #4 rebar spaced at 18 inches on center, following the guidelines set forth in IRC R506.

Please note that soil design considerations are excluded from this calculation. It is essential to consult a qualified engineer for soil analysis and site-specific recommendations.

Code reference

IRC R506

Field questions

What is the purpose of using rebar in a concrete slab?: Rebar provides tensile strength to the concrete, helping to prevent cracking and improve the overall durability of the slab.
Why is soil design excluded from this calculator?: Soil design is site-specific and requires a thorough analysis by a qualified engineer to ensure proper load-bearing capacity and stability.
What does IRC R506 cover?: IRC R506 provides guidelines for the design and construction of concrete slabs on grade, including specifications for materials, reinforcement, and placement.