How do you calculate the footing size of a building?

To calculate the footing size of a building, you first need to determine the load that the footing will support, including the weight of the structure and any live loads. Next, calculate the soil bearing capacity, which is the maximum load per unit area that the soil can safely support. Finally, divide the total load by the soil bearing capacity to find the required footing area, and adjust the dimensions (length and width) of the footing to achieve this area while ensuring stability and adherence to local building codes.