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Length imperial. Weight lb. Currency USD. Weight uses 1 lb = 0.45359237 kg. Currency converts US-dollar planning prices and does not change volumes, counts, or geometry.

18 by 12 ft slab at 6 inches

Calculate the requirements for a residential slab measuring 18 ft by 12 ft at 6 in thick 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

5.54 yd³

4.236 m³ placed+waste

Order weight

22,440 lb

10,179 kg

80 lb bags

250

6 pallets at 42 bags

60 lb bags

333

0.45 ft³ yield each

Rebar

438.00 ft

28 × 20 ft · 30 × 6 m · 322 lb

Ready-mix vs bags

$914.22

Truck $914.22 · 80 lb bags $1,687.50

Slab footprint and rebar gridLive scaled blueprint
18.00 ft12.00 ft#4 / 12 mm at 18 in OC · 6 in slab

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
ItemNetWasteOrderUnit priceLine totalSource Spec Material / Tool
Ready-mix concrete5.04 yd³10%5.54 yd³ / 4.236 m³USD$914.22Source Spec Material / Tool
Short-load feeFull load—1 truck @ 10 yd³USD$0.00Source Spec Material / Tool
80 lb pre-mix bags226.7 bags10%250 bagsUSD$1,687.50Source Spec Material / Tool
60 lb pre-mix bags302.2 bags10%333 bagsUSD$1,798.20Source Spec Material / Tool
#4 rebar sticks, 20 ft28 sticks10%31 sticks / 30 × 6 mUSD$434.00Source Spec Material / Tool
Rebar chairs117 crossings10%129 chairsUSD$36.12Source Spec Material / Tool
Tie wire rolls117 ties10%1 rollsUSD$8.00Source 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

$914.22

0.55 nominal 10 yd³ loads · 1 to order

80 lb bags

$1,687.50

60 lb alternative $1,798.20 · delivery weight 22,440 lb

Side-by-side thickness comparison at the same footprint
ThicknessOrder yd³Order m³80 lb bagsRebar ftReady-mix80 lb cost
4 in4.453.406201482$734.96$1,356.75
5 in5.003.821225482$824.59$1,518.75
6 in5.544.236250482$914.22$1,687.50
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: 18 by 12 ft slab at 6 inches

Prepared by

Date

Verified by (PE / electrician / inspector)

License number

Signature

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 18 ft by 12 ft with a thickness of 6 inches. Reinforcement is provided using #4 bars spaced 18 inches apart. 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 in residential construction.

Code reference

IRC R506

Field questions

What is the thickness of the slab?
The slab is designed to be 6 inches thick.
What type of reinforcement is used?
The slab uses #4 bars spaced 18 inches apart.
Is soil design included in this calculation?
No, soil design considerations are excluded from this calculation.
What code should I refer to for slab design?
Refer to the International Residential Code (IRC) R506 for slab design requirements.

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