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

The #4 bars provide tensile strength to the concrete slab, helping to control cracking and improve overall structural integrity.

Why is soil design excluded from this calculator?

Soil design is a complex aspect that varies significantly based on local conditions. It is recommended to consult a geotechnical engineer for soil-related assessments.

What thickness is recommended for a residential slab?

A thickness of 5 inches is commonly recommended for residential slabs, but specific requirements may vary based on load and soil conditions.

10 by 12 ft slab at 5 inches

Calculate your residential slab dimensions and reinforcement requirements with our easy-to-use calculator. Compliant 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: 10 by 12 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 for a residential slab measuring 10 ft by 12 ft with a thickness of 5 inches. It incorporates #4 bars placed at 18 inches on center for reinforcement. Please note that soil design considerations are excluded from this calculation.

For compliance, refer to the International Residential Code (IRC) R506, which outlines the requirements for concrete slabs on grade.

Code reference

IRC R506

Field questions

What is the purpose of using #4 bars in the slab?: The #4 bars provide tensile strength to the concrete slab, helping to control cracking and improve overall structural integrity.
Why is soil design excluded from this calculator?: Soil design is a complex aspect that varies significantly based on local conditions. It is recommended to consult a geotechnical engineer for soil-related assessments.
What thickness is recommended for a residential slab?: A thickness of 5 inches is commonly recommended for residential slabs, but specific requirements may vary based on load and soil conditions.