Concrete Footing Calculator

How to Use the Concrete Footing Calculator

Select round for a sonotube or circular post hole, and select square for a box-shaped footing. Enter the diameter or side length in inches, the full concrete depth in inches, and the number of identical holes. The concrete footing calculator reports cubic feet for one hole, total cubic yards for all holes, and the number of 80 lb bags. Measure the actual excavation because loose soil and irregular sides can use more material than a plan dimension suggests. Group only footings with the same shape and depth; calculate other sizes separately and add their totals. The footing estimator is a material planning tool. A qualified professional and local requirements should determine diameter, depth, bearing area, frost protection, and structural details.

Footing Calculation Formula Explained

A round footing begins with circle area: π × (diameter ÷ 2)². Multiply that area by depth to get cubic volume. A square footing uses side × side × depth. Because the inputs are inches, the calculator changes them to feet before reporting cubic feet and divides total cubic feet by 27 for cubic yards. For example, one 12-inch diameter hole 36 inches deep has an area of about 0.785 square feet and a volume of about 2.36 cubic feet. Four identical holes total 9.42 cubic feet, or 0.35 cubic yards before extra material. The post hole calculator also divides volume by a typical 0.60-cubic-foot yield for an 80 lb bag and rounds up. Actual bag yield varies, so check the product label before buying.

Common Footing Sizes

The following sizes illustrate common planning starting points, not universal requirements. Soil, frost depth, load, wind, post size, and local rules can require different dimensions.

Confirm that the bottom reaches suitable bearing soil and complies with local frost rules. Wider bases or engineered shapes need separate volume sections.

Types of Concrete Footings

A deck footing carries a concentrated post load and may use a round tube, a formed square base, or an approved system. A sonotube calculator focuses on the cylindrical part of a pier and is useful when several identical tubes are placed together. A post hole calculator applies similar geometry to poles and small supports. A fence post concrete calculator usually deals with narrower, shallower holes, but wind, gate loads, and soil still matter. Continuous strip footings under walls are different: they use length × width × depth and can be estimated as a long rectangular section. For masonry supported by a continuous base, calculate the footing first and then use the concrete block calculator for the wall units. Bring the final quantity to the concrete cost calculator for budgeting.

Inspect holes before calculating the final purchase. Bell-shaped bottoms, stepped rock, collapsed sides, and over-excavation add volume that the nominal diameter does not show. Remove loose soil and standing water by an approved method, and measure several points when a hole is irregular. For multiple piers, label each measured size rather than assuming every excavation matches the first. A short field schedule with diameter, depth, and count makes the order easier to review and reduces accidental omissions.