What is the thickness of the slab?

The slab thickness is 4 inches.

What are the dimensions of the slab?

The slab measures 10 feet by 20 feet.

What type of reinforcement is used?

The slab uses #4 bars spaced at 18 inches.

Which code does this slab design comply with?

This design complies with IRC R506 standards.

10 by 20 ft slab at 4 inches

Calculate the specifications for a residential slab measuring 10 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

2.72 yd³

2.077 m³ placed+waste

Order weight

11,000 lb

4,990 kg

80 lb bags

123

3 pallets at 42 bags

60 lb bags

163

0.45 ft³ yield each

Rebar

280.00 ft

21 × 20 ft · 28 × 6 m · 206 lb

Ready-mix vs bags

$573.15

Truck $573.15 · 80 lb bags $830.25

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	2.47 yd³	10%	2.72 yd³ / 2.077 m³	USD	$448.15	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	111.1 bags	10%	123 bags	USD	$830.25	Source Spec Material / Tool
60 lb pre-mix bags	148.1 bags	10%	163 bags	USD	$880.20	Source Spec Material / Tool
#4 rebar sticks, 20 ft	21 sticks	10%	24 sticks / 28 × 6 m	USD	$336.00	Source Spec Material / Tool
Rebar chairs	98 crossings	10%	108 chairs	USD	$30.24	Source Spec Material / Tool
Tie wire rolls	98 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

$573.15

0.27 nominal 10 yd³ loads · 1 to order

80 lb bags

$830.25

60 lb alternative $880.20 · delivery weight 11,000 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	2.72	2.077	123	308	$573.15	$830.25
5 in	3.40	2.596	153	308	$685.19	$1,032.75
6 in	4.07	3.115	184	308	$672.22	$1,242.00

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 20 ft slab at 4 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 to assist in determining the specifications for a residential concrete slab measuring 10 ft by 20 ft with a thickness of 4 inches. Reinforcement with #4 bars spaced at 18 inches is included in the design.

Please note that soil design considerations are excluded from this calculation. It is essential to consult with a qualified engineer for soil analysis and to ensure compliance with local building codes.

Code reference

IRC R506 - Concrete Slabs

Field questions

What is the thickness of the slab?: The slab thickness is 4 inches.
What are the dimensions of the slab?: The slab measures 10 feet by 20 feet.
What type of reinforcement is used?: The slab uses #4 bars spaced at 18 inches.
Is soil design included in this calculation?: No, soil design considerations are excluded from this calculation.
Which code does this slab design comply with?: This design complies with IRC R506 standards.