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

Rebar is used to provide tensile strength to concrete, which is naturally strong in compression but weak in tension. This helps prevent cracking and improves the overall durability of the slab.

Why is soil design excluded from this calculation?

Soil design is a critical aspect that depends on various factors such as soil type, load-bearing capacity, and moisture content. It should be assessed by a qualified engineer to ensure proper support for the slab.

What does IRC R506 cover?

IRC R506 provides guidelines for the design and construction of concrete slabs on grade, including requirements for thickness, reinforcement, and curing to ensure structural integrity.

How do I ensure my slab meets local building codes?

Consult with your local building authority or a licensed engineer to ensure that your slab design complies with all applicable codes and regulations in your area.

18 by 14 ft slab at 8 inches

Calculate the specifications for an 18 ft by 14 ft residential slab with #4 bars at 18 in spacing. Ensure compliance with IRC R506 guidelines. Soil design is excluded.

Formula SSC-2026.1

Formula SSC-2026.1 · 4,000 PSI

Order volume

7.66 yd³

5.856 m³ placed+waste

Order weight

31,020 lb

14,070 kg

80 lb bags

345

9 pallets at 42 bags

60 lb bags

460

0.45 ft³ yield each

Rebar

490.00 ft

31 × 20 ft · 31 × 6 m · 360 lb

Ready-mix vs bags

$1,263.78

Truck $1,263.78 · 80 lb bags $2,328.75

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	6.96 yd³	10%	7.66 yd³ / 5.856 m³	USD	$1,263.78	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	313.3 bags	10%	345 bags	USD	$2,328.75	Source Spec Material / Tool
60 lb pre-mix bags	417.8 bags	10%	460 bags	USD	$2,484.00	Source Spec Material / Tool
#4 rebar sticks, 20 ft	31 sticks	10%	35 sticks / 31 × 6 m	USD	$490.00	Source Spec Material / Tool
Rebar chairs	130 crossings	10%	143 chairs	USD	$40.04	Source Spec Material / Tool
Tie wire rolls	130 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

$1,263.78

0.77 nominal 10 yd³ loads · 1 to order

80 lb bags

$2,328.75

60 lb alternative $2,484.00 · delivery weight 31,020 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	5.05	3.862	228	539	$833.56	$1,539.00
5 in	5.70	4.361	257	539	$941.11	$1,734.75
6 in	6.36	4.859	286	539	$1,048.67	$1,930.50

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 14 ft slab at 8 inches

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Date

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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 necessary specifications for a residential concrete slab measuring 18 ft by 14 ft and 8 inches in thickness. The design incorporates #4 rebar spaced at 18 inches on center, adhering to the guidelines set forth in IRC R506.

Please note that soil design considerations are excluded from this calculation and should be evaluated separately by a qualified professional.

Code reference

IRC R506

Field questions

What is the purpose of using rebar in a concrete slab?: Rebar is used to provide tensile strength to concrete, which is naturally strong in compression but weak in tension. This helps prevent cracking and improves the overall durability of the slab.
Why is soil design excluded from this calculation?: Soil design is a critical aspect that depends on various factors such as soil type, load-bearing capacity, and moisture content. It should be assessed by a qualified engineer to ensure proper support for the slab.
What does IRC R506 cover?: IRC R506 provides guidelines for the design and construction of concrete slabs on grade, including requirements for thickness, reinforcement, and curing to ensure structural integrity.
How do I ensure my slab meets local building codes?: Consult with your local building authority or a licensed engineer to ensure that your slab design complies with all applicable codes and regulations in your area.