mate normal sack length is 2 inches
of course don't extreme loose,in such case is twice 4 inches
but whole volume its different
i used 2 inches for comparison point in picture
but porn picture present fake in all possible reference points
but don't all them
its as a play game.or a guess game
so its necessary know all the true life measure comparing item
and guess which of them match for an specific porn picture.
some time hands are very small and narrow,
other face,other wrist.,other thumb finger length,other ball sack, other gland head length don't correspond with shaft length or shaft diameter ECT
all for create confusion of reality,but its vary expensive alteration of all comparing point.
it is so complex that are some porn actor that no body know their exact dick measurement
only actress work with them and if some film scene require metric tape
but if not only as reference. their petit hands