Drawing in inches and feet

I am trying to make a drawing program that you can draw floor plans and the like with vb .net 2010.I know how to use gdi but I need to know how to draw lines that are scaled in inches and feet.Can anyone out there help me out with this problem?
I have tried the dpi x and y but it only gives me the resolution which is 96 dpi.
I seem to have gone brain dead trying to figure this out and it is probably as simple as can be.

Resolution and DPI are two different things. If the DPI is 96 then drawing 96 dots means that you've drawn an inch.

then inches would = line length /96?

Will this work to Scale this down to 1/4 inch = 1 foot
dim length as integer
length = dpix/48
I forgot to tell you that I am using vb .net 2010.