What is the significance of IRC R506?

IRC R506 provides guidelines for the design and construction of concrete slabs in residential buildings, ensuring safety and structural integrity.

Why is soil design excluded from this calculation?

Soil design is excluded because it requires specific geotechnical analysis that varies by location and is crucial for determining the load-bearing capacity of the soil.

What does #4 rebar mean?

#4 rebar refers to reinforcing bars that are 1/2 inch in diameter, commonly used in concrete construction to enhance tensile strength.

How do I ensure my slab meets local building codes?

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

14 by 20 ft slab at 4 inches

Calculate the requirements for a residential slab measuring 14 ft by 20 ft at 4 in thickness 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

3.80 yd³

2.907 m³ placed+waste

Order weight

15,400 lb

6,985 kg

80 lb bags

172

5 pallets at 42 bags

60 lb bags

229

0.45 ft³ yield each

Rebar

396.00 ft

24 × 20 ft · 34 × 6 m · 291 lb

Ready-mix vs bags

$752.41

Truck $752.41 · 80 lb bags $1,161.00

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	3.46 yd³	10%	3.80 yd³ / 2.907 m³	USD	$627.41	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	155.6 bags	10%	172 bags	USD	$1,161.00	Source Spec Material / Tool
60 lb pre-mix bags	207.4 bags	10%	229 bags	USD	$1,236.60	Source Spec Material / Tool
#4 rebar sticks, 20 ft	24 sticks	10%	27 sticks / 34 × 6 m	USD	$378.00	Source Spec Material / Tool
Rebar chairs	140 crossings	10%	154 chairs	USD	$43.12	Source Spec Material / Tool
Tie wire rolls	140 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

$752.41

0.38 nominal 10 yd³ loads · 1 to order

80 lb bags

$1,161.00

60 lb alternative $1,236.60 · delivery weight 15,400 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	3.80	2.907	172	436	$752.41	$1,161.00
5 in	4.75	3.634	214	436	$784.26	$1,444.50
6 in	5.70	4.361	257	436	$941.11	$1,734.75

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 20 ft slab at 4 inches

Prepared by

Date

Verified by (PE / electrician / inspector)

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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 14 ft by 20 ft with a thickness of 4 inches. The design incorporates #4 rebar spaced at 18 inches on center, which is compliant with IRC R506 guidelines for residential concrete slabs.

Please note that soil design considerations are excluded from this calculation. It is essential to evaluate the underlying soil conditions to ensure proper support for the slab.

Code reference

IRC R506

Field questions

What is the significance of IRC R506?: IRC R506 provides guidelines for the design and construction of concrete slabs in residential buildings, ensuring safety and structural integrity.
Why is soil design excluded from this calculation?: Soil design is excluded because it requires specific geotechnical analysis that varies by location and is crucial for determining the load-bearing capacity of the soil.
What does #4 rebar mean?: #4 rebar refers to reinforcing bars that are 1/2 inch in diameter, commonly used in concrete construction to enhance tensile strength.
How do I ensure my slab meets local building codes?: Consult with a licensed engineer or local building authority to verify that your slab design complies with all applicable codes and regulations.