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Concrete Footing Calculator

Cubic yards and bags of concrete for continuous footings or round deck and pier footings.

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Call your building department for the frost depth first

Footing depth is set locally, not by a national rule, and inspectors check it before the pour. A deck footing that sits above the frost line can heave a joist out of level in one winter. Ask for the required depth and minimum diameter before you rent an auger.

Sizing and figuring concrete for footings

A continuous footing is a long rectangular beam of concrete, so its volume is length × width × depth, with width and depth converted from inches to feet. The International Residential Code's Table R403.1 sets minimum footing widths by soil and number of stories; 12 in. wide by 6 in. thick is the bare minimum, and 16 to 24 in. wide by 8 in. is common for house walls.

Round pier and deck footings are cylinders: volume = π × (diameter ÷ 2)² × depth for each hole. Footings must extend below your local frost line, which your building department sets and which can run from 12 in. in the South to 48 in. or more up north.

Divide cubic feet by 27 for cubic yards. Bag counts use QUIKRETE's published yields of 0.60 cu ft per 80 lb bag and 0.45 cu ft per 60 lb bag. The 10% extra covers trenches dug a little wide and holes that flare at the top, which is the norm rather than the exception.

Where these numbers come from

The formulas and default values in this calculator are based on:

  • International Residential Code (IRC) Section R403.1 footing requirements
  • QUIKRETE Concrete Mix No. 1101 data sheet bag yields

These are planning estimates. Check product labels, your local building code, and a licensed contractor before you buy materials or build.

Frequently asked questions

How wide should a footing be?

A common rule is twice the width of the wall it supports, and never less than the IRC minimum for your soil and number of stories. An 8 in. block wall often sits on a 16 in. wide footing. Local codes and soil conditions can require more.

Do deck footings need to be bell-shaped?

Some jurisdictions allow a straight cylinder poured in a tube form; others want a wider base pad or a flared bottom for bearing area. Your deck permit drawings will say which, and the extra concrete for a bell is worth adding to this estimate.

Should footings have rebar?

Continuous footings usually get two runs of #4 bar, and many codes require it in seismic areas. Use the rebar calculator to add it up, and keep the bar at least 3 in. from the soil.

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