This is an interesting topic-
Professional porn producers select men who have over-endowed sized dicks that are 8+inches or larger... Realize it's simply marketing. That's why you'll rarely see the biggest men in porn show their true measurements on photos or on video because of sales - Think about it!
A stiff ruler, a tape measure used, or some object that can be identified with to compare to against their cocks might be used sometimes as reference, but these guys always come up short or slightly above average in size - But not the 12+incher they might claim in their advertising.
Believe me I possess a 10-incher and I know what a dick this size looks like...
Moreover, when you use the wide angle lens, or fish eye lens for videotaping of these fucking scenes of these huge porn stars, that too adds a distorted view of their extra large size as well. We must remember that this is for our amusement, and most men don't come close to these porn actors sizes; however, a few men here on LPSG are in the 10+inch class size.