Specifications for designing footings are done according to the standard IS 456:2000. If you follow these forms for designing you should consider several points. It is very important to pay attention to the thickness at the edge of footing the moments and forces. The calculations depend on placement of the footings and whether they are in reinforced and plain footings. Also, there is a different way of calculating the stresses in footings.
Specifications for Designing Footings
This post will be very helpful for all those interested in constructing footings. For more detailed information you can read the text on the link applied below.