How do I get true dimensions in photoshop?

I designed something In photoshop that I need to print out to specific dimensions. Using the rulers function in photoshop I made the image. However when I view the image at full size in photoshop I realize that the rulers are not displaying true inches and consequently my image is enormous.
A. How do I get the rulers to display true inches?
B. The only printer I have access to is connected to a PC that does not have photoshop, how can I transfer the file to that computer and print it while preserving the original dimensions?