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

Using #4 bars helps to reinforce the concrete slab, providing additional tensile strength to prevent cracking and improve load-bearing capacity.

Why is soil design excluded from this calculation?

Soil design is a separate consideration that depends on the specific site conditions. It is important to conduct a soil analysis to determine the appropriate foundation design.

What thickness is recommended for a residential slab?

A thickness of 6 inches is commonly recommended for residential slabs, providing adequate strength for typical loads.

10 by 18 ft slab at 6 inches

Calculate the requirements for a residential slab measuring 10 ft by 18 ft at 6 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

4.73 yd³

3.613 m³ placed+waste

Order weight

19,140 lb

8,682 kg

80 lb bags

213

6 pallets at 42 bags

60 lb bags

284

0.45 ft³ yield each

Rebar

368.00 ft

26 × 20 ft · 26 × 6 m · 270 lb

Ready-mix vs bags

$779.78

Truck $779.78 · 80 lb bags $1,437.75

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	4.30 yd³	10%	4.73 yd³ / 3.613 m³	USD	$779.78	Source Spec Material / Tool
Short-load fee	Full load	—	1 truck @ 10 yd³	USD	$0.00	Source Spec Material / Tool
80 lb pre-mix bags	193.3 bags	10%	213 bags	USD	$1,437.75	Source Spec Material / Tool
60 lb pre-mix bags	257.8 bags	10%	284 bags	USD	$1,533.60	Source Spec Material / Tool
#4 rebar sticks, 20 ft	26 sticks	10%	29 sticks / 26 × 6 m	USD	$406.00	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

$779.78

0.47 nominal 10 yd³ loads · 1 to order

80 lb bags

$1,437.75

60 lb alternative $1,533.60 · delivery weight 19,140 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	3.86	2.949	174	405	$761.37	$1,174.50
5 in	4.29	3.281	194	405	$708.07	$1,309.50
6 in	4.73	3.613	213	405	$779.78	$1,437.75

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 6 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 concrete slab measuring 10 ft by 18 ft with a thickness of 6 inches. The design incorporates #4 rebar spaced at 18 inches on center, ensuring structural integrity.

Please note that soil design considerations are excluded from this calculation. For compliance, refer to the International Residential Code (IRC) R506 for guidelines on concrete slabs.

Code reference

IRC R506

Field questions

What is the purpose of using #4 bars in the slab?: Using #4 bars helps to reinforce the concrete slab, providing additional tensile strength to prevent cracking and improve load-bearing capacity.
Why is soil design excluded from this calculation?: Soil design is a separate consideration that depends on the specific site conditions. It is important to conduct a soil analysis to determine the appropriate foundation design.
What thickness is recommended for a residential slab?: A thickness of 6 inches is commonly recommended for residential slabs, providing adequate strength for typical loads.