Calculate Size for Mac

From Pixture Studio:

Contextual menu plug-in calculates the total size of the selected files and folders. It can calculate the total size of selected folders and files. It can include invisible files (such as folder's custom icon) for the calculation. You can get more precise size than Finder's "Get Info" dialog. It can display the progress information while calculating. You can cancel the operation any time during the calculation. By setting the progress information display mode to OFF, it can performe high speed calculation. Expand mode shows you the data fork and resource fork size of the total size.