printing textboxes location

Question

hi there, i'm working at an app - windows forms that contains many textboxes. the textboxes have a location on an A5 paper. i have also a print button that must print the content of th textboxes on an A5 paper. But it actually prints the content a bit smaller than the needed papersize. The question is: how to specify the size of the rectangle created by the textboxes in mm or cm so it won't change at different PC's. Thank YOU in advance.