How to calculate footer excavations

Written by timothy burns
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How to calculate footer excavations
Planning is key to success in building construction. (Waterside Excavator image by Van Ness from

When laying a building's foundation, the footer is the base of the foundation on which rests the weight of the entire building. The footing prevents the foundation from shifting once the building is constructed. The depth of the foundation will be determined by local building codes. The width of the foundation and footer will also be determined by local building codes, the type of soil on which the building is constructed, and the building's overall size. Once the size and depth of the foundation and building are known, calculations regarding the foundation size, and volume of the earth to be excavated are a matter of simple algebra.

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Things you need

  • Blueprints
  • Excavating equipment
  • Earth and debris removal plan
  • Standard calculator

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  1. 1

    Determine the length, width, and depth of the area to be excavated. In the case of a residential home with a basement, this dimension would be equal to the total volume of the lowest level or basement of the building. In the case of a residential home without a basement, this dimension would include the depth of the foundation multiplied by the width of the foundation multiplied by total linear footage of foundation wall to be constructed. These dimensions can be ascertained from the blueprints.

  2. 2

    Calculate the measurement of the foundation footing from the relationship between the width of the foundation wall and the overall width of the footing. In residential settings, the footing is twice the width and the same thickness of the foundation wall. For example if the residential homes foundation wall is 8 inches thick, the foot thing would be 16 inches wide and 8 inches tall.

  3. 3

    Add to the volume of earth which must be excavated for the basement/lower-level of the building the additional distance which must be used to allow for the footing to be framed and poured. In the example of a residential home, allowances for the footing would add an additional 3 to 4 feet of width and length to the hole which must be created.

  4. 4

    Calculate the total volume of berth to be removed by multiplying the length times width times height of the hole to be cleared. Before beginning excavation, devise a plan for removal of excavated earth and debris from the building site.

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