GIMP 2.10 Won't print picture in selected size

[PeaceLuth]

I'm making correction and text additions to numerous photographs. All are imported from JPG files and set to 8 1/2 X 11 inch landscape at 300 dpi.
After making the necessary edits I save the picture in GIMP's default XCF file format. I then check the image size and canvas size to make sure they are the same, usually 8 1/4 X 10 3/4 inches to account for printer margins. I then print out a sample on plain paper. I'll use either an HP Envy 5055 inkjet or our Konica-Minolta bizhub C558. I'll check all the setting of the printers and then print.

I've yet to get a print that is 8 1/4 X 10 3/4. The print is usually 6 1/5 X 8 3/4. What gives?

[rich2005]

Just a bit of background, Gimp is developed in linux, the Gimp developers use linux, linux uses a different printing system to Windows.
For Windows there is an additional plugin 'winprint' I don't think it has much changed in years, just gets 'bolted-on' by the two or three people who actually compile the Windows Gimp.

I am a very-occasional Win user, I do all my printing in linux so please take the following as just 'maybe / might work'

A screenshot for reference. https://i.imgur.com/Iv1Dz0C.jpg

(1) A 300 ppi US letter size image (landscape) with print size set to 10.5 x 8.25 gives a printing resolution of 309 ppi
(2) Nice printers you have, I assume they are all set up as required.
(3) In the print dialog it looks to me that all you get is a portrait option shrinking the size to 8 x 6 @ 412 ppi Your printer setup might print this Landscape and Centered ( I do not know)

Next screenshot: https://i.imgur.com/Y7V6E5H.jpg

(4) If Gimp wants to print Portrait, let it. Rotate the image 90 deg and the print dialog now shows almost 8 x 10 @ 323 ppi Why not 309 ppi ? The printer imposes a wider margin at the bottom required for paper feed. All depends on the printer. You can set ignore Page margins and risk a truncated print.

EDIT: Told you I was just an occasional Win user. Totally forgot that the page setup is separate from the Print dialogue (unlike linux) Did you set up something like this: https://i.imgur.com/RF69C3z.jpg Still not working ? Jump to the end for alternatives.

Just in case you are not using Gimp 2.8 but are using Gimp 2.10 screenshot: https://i.imgur.com/flCYKVC.jpg

Just the same as for Gimp 2.8 but the bottom of the print dialogue is cut off. This is a function of the dark / grey themes. Go into Edit -> Preferences ->Themes and set the theme to 'System'

Alternatives and better bets
Do not use Gimp for printing. Use some other application such as XnView or IrfanView.
Print from Gimp to a PDF. Use a PDF viewer program for printing.

Seem to recall the last time I tried printing from a Windows Gimp. The exact opposite of the problem. Wanted a 6x4 print, all I could get was a full page (A4)