Footing calculator
Concrete Footing Calculator
Calculate concrete needed for foundation footings, strip footings, and trenches. Estimate volume, bags, waste factor, and cost for continuous footing pours.
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How to Calculate Concrete for Footings
Foundation footings are continuous strips of concrete that distribute building loads to the soil. Calculate footing volume using: Volume = length × width × depth
For example, a house perimeter with 120 linear feet of footing, 24 inches wide and 12 inches deep, requires:
Volume = 120 × 2 × 1 = 240 cubic feet = 8.89 cubic yards
Common Footing Dimensions
- Residential walls: 12-24 inches wide, 8-12 inches deep
- Load-bearing walls: 18-24 inches wide, 12 inches deep
- Non-load-bearing walls: 12-16 inches wide, 8 inches deep
- Pier footings: 24-36 inches square, 12-24 inches deep
Footing Design Considerations
Footing size depends on soil bearing capacity and structural loads. Always check local building codes for minimum requirements. Footings must extend below the frost line to prevent freeze-thaw damage. In cold climates, this is typically 36-48 inches deep.
Reinforcement with rebar is typically required for footings supporting structural walls. Use #4 or #5 rebar placed horizontally with vertical dowels extending into the foundation wall.
Frequently Asked Questions
How wide should a footing be?
Footing width depends on the load and soil type. A general rule is 2× the wall thickness for light-frame construction. For example, a 2×6 wall (5.5 inches) needs a minimum 12-inch wide footing. Always check local building codes for specific requirements.
How deep should footings be?
Footings must extend below the frost line to prevent heaving. In most regions, this is 12-48 inches. The footing thickness is typically 8-12 inches. Check your local building department for the required frost depth in your area.
Do footings need rebar?
Most building codes require reinforcement for footings supporting structural walls. Typically, two horizontal #4 rebar bars are placed in the footing with vertical dowels extending up to tie into the foundation wall. Consult your local building department for specific requirements.
How much concrete for a 20x20 garage footing?
A 20x20 garage has 80 linear feet of perimeter footing. With 24-inch wide × 12-inch deep footings: 80 × 2 × 1 = 160 cubic feet = 5.93 cubic yards. Add 10% waste = 6.5 cubic yards of concrete.