Issues with Image size, Canvas size

[rhenkel]

[I’ve been using GIMP for a couple of months.  After creating a new document 11x17 inches, 300dpi, I export a pdf and take it to the printer who says the document is actually over 50” wide.  I’ve spent a lot of time trying to get this right, including watching several instructional videos. 

Maybe when I bring artwork that was shot on my iPhone into GIMP the canvas size changes?  I don’t understand what’s happening here.

Can you help?

Thank you.
I’m using a MacBook Pro, Catalina 10.15.7

[Ofnuts]

How big is the image in pixels?

[rich2005]

The first thing to check with your image open is Image -> Print Size
It should look like (1) Width / Height 17 x 11 in  resolution 300 ppi  That gives an image size in pixels 5100 x 3300 ppi. 

   

Where does the printer get the "more than 50" inches wide" ?  If the resolution is 100 ppi (2) then your 5100 x 3300 ppi image will send information to print that large size.

   

Why might the printer think your PDF is 100 ppi ? Open any PDF in Gimp and the default resolution is 100 ppi (3) This is normal with PDF it is a portable format for viewing electronic documents. The PDF viewer handles viewing size. Using Gimp then the user has to set the resolution (4)   Note the reported document size 17" x 11" is embedded in the PDF and is independent of the set resolution.

   

You can check that in a PDF viewer,the document properties will report the size when the PDF was created. (5) The printing company should know that and print accordingly.

Gimp and PDF Using MacOS and assuming Gimp 2.10.14  
Gimp does not make good PDF's. Especially when it comes to text, where font and formatting might be lost.  If text is an important part of the image then use the DTP program Scribus which correctly embeds text in a PDF.
Otherwise consider giving the printing company a tiff or even for that size image a jpeg.