How do I get true dimensions in photoshop?

A: Maybe the rulers are set to pixels or centimeters instead of inches? (Sorry I don’t have Photoshop on my work machine and can’t tell you exactly where you can change that setting in the menus).

B: Save as PDF

whats your resolution set to?

if its something like 300dpi (which it should be for print) on your computer its going to look massive at 100% size.

Full size on your screen is not accurate as pixels vary in size from nomitor to monitor. Specify the print size in the umage menu, select image size. You can select both resolution and print size. I will post the control panel

You can maintain print size while resampling resolution.
Hope this helps.

I think jaytkay might have meant picas, not pixels. But picas (10=1 inch), centimeters, or even pixels would result in a smaller image than expected.
Anartist is correct. You can’t simply measure the physical size on the screen with a ruler.
To confirm size go to Image>image size. You can also resize there if needed.
You can choose ruler preferences at Edit>preferences>rulers. Also, click the square where the vertical and horizontal ruler meet to get options.
You will need to save your psd (photoshop document) as a jpg or pdf to make sure you can open it in another program. This will flatten your layers, but that’s OK if you only need to print it.

_I think jaytkay might have meant picas, not pixels. But picas (10=1 inch), centimeters, or even pixels would result in a smaller image than expected. _

Thank you for the correction

DOH!

Trust what the rulers are telling you, not the size on the screen. If you are printing to a desktop printer the resolution needs to be at least 200 dpi, preferably 300 dpi for a nice image.