Deck Footing Chart

Footing size depends on how much deck area each post carries (its tributary area) and the soil. This chart gives typical footing diameters for average soil at common deck loads.

Footing diameter Supports up to
8 in about 20 sq ft of deck
10 in about 30 sq ft
12 in about 45 sq ft
16 in about 80 sq ft
Depth follows frost. Footings must extend below your local frost line so they do not heave. Weaker soil or larger tributary areas call for wider footings.

Size the concrete with the Concrete Footing Calculator and read Deck Footing Size Guide.

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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.