IRC R506 outlines the requirements for concrete floors on the ground, including specifications for thickness, reinforcement, and other construction practices to ensure structural integrity.

Why is soil design excluded from this calculator?

Soil design is a critical aspect that depends on local soil conditions and load-bearing capacity. It is recommended to consult a geotechnical engineer for soil analysis.

What does #4 bars at 18 inches mean?

#4 bars refer to rebar with a diameter of 0.5 inches, and spacing them at 18 inches means the bars are placed 18 inches apart within the slab for reinforcement.

10 by 18 ft slab at 5 inches

Calculate the specifications for a residential slab measuring 10 ft by 18 ft at 5 inches thick with #4 bars at 18 inches apart. Ensure compliance with IRC R506 standards.

Formula SSC-2026.1

Formula SSC-2026.1 · 4,000 PSI

Order volume

3.06 yd³

2.336 m³ placed+waste

Order weight

12,375 lb

5,613 kg

80 lb bags

138

4 pallets at 42 bags

60 lb bags

184

0.45 ft³ yield each

Rebar

256.00 ft

20 × 20 ft · 20 × 6 m · 188 lb

Ready-mix vs bags

$629.17

Truck $629.17 · 80 lb bags $931.50

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	2.78 yd³	10%	3.06 yd³ / 2.336 m³	USD	$504.17	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	125.0 bags	10%	138 bags	USD	$931.50	Source Spec Material / Tool
60 lb pre-mix bags	166.7 bags	10%	184 bags	USD	$993.60	Source Spec Material / Tool
#4 rebar sticks, 20 ft	20 sticks	10%	22 sticks / 20 × 6 m	USD	$308.00	Source Spec Material / Tool
Rebar chairs	91 crossings	10%	101 chairs	USD	$28.28	Source Spec Material / Tool
Tie wire rolls	91 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

$629.17

0.31 nominal 10 yd³ loads · 1 to order

80 lb bags

$931.50

60 lb alternative $993.60 · delivery weight 12,375 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	2.44	1.869	110	282	$528.33	$742.50
5 in	3.06	2.336	138	282	$629.17	$931.50
6 in	3.67	2.803	165	282	$730.00	$1,113.75

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: 10 by 18 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 specifications for a residential slab measuring 10 ft by 18 ft and 5 inches thick, reinforced with #4 bars spaced 18 inches apart. While this design adheres to IRC R506 guidelines, please note that soil design considerations are excluded from this calculation.

Ensure that all local building codes and regulations are followed, and consult a licensed engineer for a comprehensive design review.

Code reference

IRC R506 - Concrete Floors on Ground

Field questions

What is IRC R506?: IRC R506 outlines the requirements for concrete floors on the ground, including specifications for thickness, reinforcement, and other construction practices to ensure structural integrity.
Why is soil design excluded from this calculator?: Soil design is a critical aspect that depends on local soil conditions and load-bearing capacity. It is recommended to consult a geotechnical engineer for soil analysis.
What does #4 bars at 18 inches mean?: #4 bars refer to rebar with a diameter of 0.5 inches, and spacing them at 18 inches means the bars are placed 18 inches apart within the slab for reinforcement.