54mm, but we're not being that picky.
Condom listed sizes apparently don't correlate to an actual measured diameter. Maybe some arbitrary partially stretched size? I dunno.
Trojan lists the Magnum as 54mm/2.13" base width. I have one holdout sitting in my nightstand....My ruler shows 1.5" measured in the package.
They show the XL as 56mm/2.2" base width. The ones in my drawer measure barely 1-5/8". As previously mentioned, the head area is wider, which helps a lot, but these are still uncomfortable on my 6" girth, and definitely are not the stated 8.3" length either. If they were, I must be 9-1/2"......lolz.....