FWIW dept... You can ask "Dr StartPage" (He won't sell your personal info like Dr Google does...) about the "proper" procedures for measuring, which use the pubic bone as a reference point, and thus supposedly aren't heavily impacted by body fat...

Two that came up from me, that are both at least somewhat reputable sites:

https://www.webmd.com/men/what-is-the-a ... penis-size

https://www.verywellhealth.com/how-to-m ... ize-906786

WheelyFixed