Area is commonly described as the extent of a two-dimensional surface enclosed within a specified boundary. Calculating area is fairly straight forward for well-defined regions, like regular polygons and symmetrical circles and ellipses. Finding the area for irregular regions requires the application of calculus. In fact, it is with the assistance of calculus that even a common formula like for the area of an ellipse is derived. 

Below is a table of commonly used area conversion factors.

Standard units = Square centimeter (cm²) for metric
                            Square inch (ft²) for SAE