How much concrete do I need for a foundation?

Multiply perimeter × wall height × wall thickness (in feet) and divide by 27 for cubic yards. For a slab, multiply length × width × depth and divide by 27.

How deep should a foundation be?

Footings must extend below the local frost depth. In Florida, 0 inches is sufficient; in Minnesota, footings must be at least 60 inches deep to prevent frost heave.

What rebar spacing is standard for residential foundations?

IRC requires a minimum of #4 rebar at 16 inches on center vertically and horizontally for most residential foundations.

Do I need a vapor barrier under a concrete slab?

Yes. A 6-mil polyethylene vapor barrier is required under slabs per IRC R506.2.3 to prevent moisture migration from soil into the concrete.

How many anchor bolts are needed?

Anchor bolts should be spaced no more than 6 feet apart and within 12 inches of each end of a sill plate per IRC R403.1.6.

Foundation Calculator

Calculate concrete cubic yards, rebar linear feet, and formwork area for slab, stem wall, and pier foundations. Includes frost depth guidance by region.

Length (ft)

Width (ft)

Wall Height (ft)

Wall Thickness (in)

Concrete (cu yd)

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Rebar Linear Feet —

Formwork Area —

Extended More scenarios, charts & detailed breakdown ▾

Length (ft)

Width (ft)

Slab Depth (in)

Waste %

Concrete (cu yd)

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Slab Area (sq ft) —

80 lb Bags Alt. —

Professional Full parameters & maximum detail ▾

Length (ft)

Width (ft)

Wall Height (ft)

Wall Thickness (in)

Rebar Spacing (in OC)

Gravel Base Depth (in)

Frost Depth Region

Concrete & Rebar

Concrete (cu yd) —

Rebar Linear Feet —

Site Prep

Gravel Base (cu yd) —

Vapor Barrier (sq ft) —

Anchor Bolts (est.) —

Min. Frost Depth —

How to Use This Calculator

Enter foundation length, width, height, and wall thickness.
Use Extended tabs for slab, stem wall+footing, or pier foundation types.
Switch to Professional for rebar spacing, gravel base, vapor barrier, anchor bolts, and frost depth by region.

Formula

Stem Wall Concrete: (Perimeter × Height × Thickness_ft) ÷ 27 = cu yd

Slab: (L × W × Depth_ft) ÷ 27 = cu yd

Pier: (π × r² × h × count) ÷ 27 = cu yd

Example

Example: 40 ft × 30 ft foundation, 3 ft tall walls, 8 in thick → perimeter 140 ft → 140 × 3 × 0.667 = 279.6 cu ft → 10.4 cu yd of concrete.

Frequently Asked Questions

Multiply perimeter × wall height × wall thickness (in feet) and divide by 27 for cubic yards. For a slab, multiply length × width × depth and divide by 27.
Footings must extend below the local frost depth. In Florida, 0 inches is sufficient; in Minnesota, footings must be at least 60 inches deep to prevent frost heave.
IRC requires a minimum of #4 rebar at 16 inches on center vertically and horizontally for most residential foundations.
Yes. A 6-mil polyethylene vapor barrier is required under slabs per IRC R506.2.3 to prevent moisture migration from soil into the concrete.
Anchor bolts should be spaced no more than 6 feet apart and within 12 inches of each end of a sill plate per IRC R403.1.6.

Related Calculators

Sources & References (5) ▾

ACI 332 – Requirements for Residential Concrete Construction — American Concrete Institute
IRC Chapter 4 – Foundations — ICC / IRC
ICF Builders Handbook — ICF Manufacturers Association
NAHB Builders Manual — National Association of Home Builders
USDA Rural Development – Foundations for Farm Buildings — USDA Rural Development