Image scaling question

[Cosmopsis]

Hi, I'm completely new to photo editing and I'm so confused by this problem. Will be very grateful if anyone can explain what's going on!

I'm trying to make image 2 the same width as image 1. The images each individually measure about 45mm, but image 2 is somehow still smaller?

When I cut and paste image 2 onto image 1, it shows as about 25mm, when it was showing as about 45 mm when it was a separate file.

I assume I'm fundamentally misunderstanding something but I have no idea what.

   
   
   

[Ofnuts]

What counts is the size in pixels. The size in physical units (inches/mm) is fairly virtual.

See https://www.gimp-forum.net/Thread-Image-size-in-Gimp