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

Rebar is used to reinforce concrete slabs, providing additional tensile strength and helping to prevent cracking.

Why is soil design excluded from this calculator?

Soil design is excluded because it requires specific geotechnical analysis based on site conditions, which is beyond the scope of this calculator.

What does IRC R506 cover?

IRC R506 covers the requirements for concrete slabs, including thickness, reinforcement, and placement to ensure structural safety and performance.

12 by 10 ft slab at 5 inches

Calculate the specifications for a residential slab measuring 12 ft by 10 ft at 5 in thick 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

2.04 yd³

1.557 m³ placed+waste

Order weight

8,250 lb

3,742 kg

80 lb bags

3 pallets at 42 bags

60 lb bags

123

0.45 ft³ yield each

Rebar

174.00 ft

16 × 20 ft · 16 × 6 m · 128 lb

Ready-mix vs bags

$461.11

Truck $461.11 · 80 lb bags $621.00

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	1.85 yd³	10%	2.04 yd³ / 1.557 m³	USD	$336.11	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	83.3 bags	10%	92 bags	USD	$621.00	Source Spec Material / Tool
60 lb pre-mix bags	111.1 bags	10%	123 bags	USD	$664.20	Source Spec Material / Tool
#4 rebar sticks, 20 ft	16 sticks	10%	18 sticks / 16 × 6 m	USD	$252.00	Source Spec Material / Tool
Rebar chairs	63 crossings	10%	70 chairs	USD	$19.60	Source Spec Material / Tool
Tie wire rolls	63 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

$461.11

0.20 nominal 10 yd³ loads · 1 to order

80 lb bags

$621.00

60 lb alternative $664.20 · delivery weight 8,250 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	1.63	1.246	74	191	$393.89	$499.50
5 in	2.04	1.557	92	191	$461.11	$621.00
6 in	2.44	1.869	110	191	$528.33	$742.50

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: 12 by 10 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 assists in determining the necessary specifications for a residential concrete slab, specifically a 12 ft by 10 ft slab with a thickness of 5 inches and #4 rebar spaced 18 inches apart. Please note that soil design considerations are excluded from this calculation.

For compliance with the International Residential Code (IRC) R506, ensure that all materials and construction practices meet the required standards for durability and structural integrity.

Code reference

IRC R506

Field questions

What is the purpose of using rebar in a concrete slab?: Rebar is used to reinforce concrete slabs, providing additional tensile strength and helping to prevent cracking.
Why is soil design excluded from this calculator?: Soil design is excluded because it requires specific geotechnical analysis based on site conditions, which is beyond the scope of this calculator.
What does IRC R506 cover?: IRC R506 covers the requirements for concrete slabs, including thickness, reinforcement, and placement to ensure structural safety and performance.