The actual feasibility size estimate is performed on the Sizing tab. For new feasibility solutions, the Sizing method defaults to Size Bin (a rough order of magnitude, t-shirt type of estimate that calculates the estimated size using size “bins” ranging from Very Small to Very Large, calculated from the range of project sizes from your project’s chosen trend group (on the Project Settings tab). The estimated value for each size bin is simply the average for each bin. Once you have chosen is size bin, the calculated size is shown in parentheses after the Bin Size label on the Sizing tab and in the Size label field on the Assumptions tab.
Because each trend group is based on multiple projects, each with their own characteristics and size ranges, changing the trend group will change the calculated size for a given “bin”. So, for example, a Medium Business system might be 142K Base size units (a normalized measure of size roughly equivalent to a line of code). A Medium Avionics system would be closer to 180K base size units.
For more detailed guidance on using the sizing techniques and fields on the Sizing tab, see the Sizing tab topic in this user guide.