Give the only reference is his thumb, and looking at the average width of the male thumb is .75 inch. And using photoshop he is about 8 1/4 thumbs which to use math means he is 6.2 in length.
The length of his thumb can be argued but again giving the average size of a thumb to be 3 inches and his length is about 3/5ths of his thumb, I assume that mease diamater wise he is 1.8 inches. Which get the general circumference, 1.8 x 3.141592653589793 (pie) = 5.65 inch.
Given it's not a perfect circle I would say girth wise he is 5.35.
Final
Length = 6.2
Girth = 5.35
So you are above average, not very well hung but still pretty nice. No women would complain (save for size queens) and some may even give a bit of a gasped look.
Next time post a comparison shot.