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Monolithic Slab Foundation Cost Calculator

Calculate costs for poured concrete slabs with thickened edges. Generates material lists for gravel, vapor barrier, mesh, and concrete with excavator rental estimates.

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Category Foundation & Concrete
Slab (Core)
Beam
Dimensions
Structural Details (Inches)
Project Add-ons
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About

Monolithic slabs are the most common foundation type for garages, sheds, and homes in warmer climates. They consist of a single pour of concrete that forms both the floor and the structural footings (thickened edges). This complexity makes simple "length x width" calculators insufficient. This professional tool calculates the differential volume of the slab core versus the perimeter beam. It provides a comprehensive project budget that includes the sub-base (gravel), moisture protection (vapor barrier), reinforcement mesh, and even heavy machinery rental costs. The output converts aggregate volumes into tonnage for precise ordering.

slab calculator concrete estimate monolithic foundation construction budget excavation cost

Formulas

The total concrete volume Vtotal is the sum of the inner slab volume and the perimeter beam volume:

Vslab = (L − 2wb) × (W − 2wb) × Dslab
Vbeam = Perimeter × wb × Dbeam

Reference Data

ComponentFunctionStandard SpecDensity / Coverage
Slab CoreMain Floor4" - 6" ThickConcrete
Thickened EdgeLoad Bearing12" - 18" DepthConcrete
Gravel BaseDrainage4" Compacted1.4 Tons / yd3
Vapor BarrierMoisture Stop6 mil PolyArea + 10% overlap
Wire MeshCrack Control6x6 - 10/10Area + 10% overlap

Frequently Asked Questions

A thickened edge (or turned-down edge) is the perimeter of the slab that is deeper than the center. It acts as a footing to support the weight of the exterior walls and prevents pests or frost from undermining the slab.
A standard base is 4 inches of compacted crushed stone. This tool calculates the cubic volume and converts it to tons (approx 1.4 - 1.5 tons per cubic yard) because quarries sell aggregate by weight, not volume.
For slabs larger than 20x20 ft, an excavator or skid steer is highly recommended. The "Labor & Equipment" section of this tool estimates a 1-2 day rental for site prep and grading.