I didn’t understand the question so I asked for a link to that site.
From that link
Q. What file size do I need to upload?
A. We need a file size of over 17MB when uncompressed (this is likely to have a compressed JPEG size of 3-5MB). Opening a JPEG in an image program such as Adobe Photoshop will show you the uncompressed (open) file size.
It’s a strange formulation. What they probably mean is the size of an uncompressed image. The disk file contains a lot of other stuff. The image size should be then 17/3=5.7MB.
George