Concrete Footing Calculator
Calculate concrete volume, bags, and cost for strip footings and isolated pad footings — with support for multiple pad counts.
Footings
Strip footings and isolated pad footings
Inputs
Typ. 2× wall thickness
Results
How to Use the Concrete Footing Calculator
Select the footing type — strip or pad. For strip footings, enter the total perimeter length, width, and depth. For pad footings, enter the pad count, length, width, and depth. The calculator returns concrete volume in cubic yards and cubic metres, equivalent bag count, and optional material cost.
How It Calculates
Strip footings use a continuous volume formula:
Pad: Volume (cu yd) = Count × L (ft) × W (ft) × D (ft) / 27
A 10% waste factor is typically recommended for footings due to formwork irregularities and trench over-excavation.
What to Know Before You Calculate
- Perimeter vs. linear footage: For strip footings, measure the total run of footing — not just the building perimeter — including any interior load-bearing walls.
- Depth to frost line: Footings must extend below the frost line for your region. In colder climates this may be 48 inches or more.
- Soil bearing capacity: Footing width must be sized to keep bearing pressure within what the soil can support. Sandy soil needs wider footings than rock.
- Rebar requirements: Most footings require rebar. Use the Rebar Calculator to size reinforcement separately.
Common Mistakes
- Using the building footprint as perimeter. Footings wrap the inside of the forms, not the building exterior edge-to-edge.
- Not accounting for interior footings. Calculate interior load-bearing footings separately and add to the perimeter total.
- Underestimating depth. If the trench bottom is uneven, average the depth at multiple points — or use the deepest point with a slight overage.
- Ordering short. For footings, order at least 5–10% extra. A short pour that cures before the truck returns is a costly repair.
Frequently Asked Questions
How do I calculate concrete for a strip footing?
Multiply the total perimeter length (ft) × footing width (ft) × footing depth (ft) to get cubic feet, then divide by 27 for cubic yards. For example, a 120 ft perimeter footing at 24 in wide × 12 in deep: 120 × 2 × 1 / 27 = 8.89 cu yd.
What is the minimum footing size for a residential building?
Most residential building codes require footings at least 8–12 inches deep and wide enough to spread the load — typically 16–24 inches for single-story, more for multi-story. Always check your local building code and soil bearing capacity.
What is the difference between a strip footing and a pad footing?
A strip (continuous) footing runs the full perimeter and supports load-bearing walls. A pad (isolated) footing is a discrete square or rectangular block that supports a single column or post. Pad footings are common under deck posts and steel columns.
Should I include the footing under interior walls in the calculation?
Yes. If interior load-bearing walls require continuous footings, measure and include their total linear footage. Interior footings are often narrower and shallower than perimeter footings, so calculate them separately.
Related Calculators
Disclaimer: Results are estimates based on standard formulas. Footing dimensions, concrete strength, and depth requirements must be verified by a licensed engineer or designer before construction.
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