[i'm a guy]
Length doesn't matter half as much as people like to think.
from my experiences, girls say, girth matters more. If you can get a girl really ho**y with the foreplay and naughty talk, she'll won't care about ur penis length.
if you think ur under average,i think its an idea NOT to tell a girl ur length during dirty talk because;
a)this is probably the only time size matters. The larger yours is, the more the girls imagination will run-dnt tell her, keep her wondering
b) instead of quoting a figure, show a figure! let her estimate, girls often overestimate.
Note:
guys nearly always overestimate, and it is guys who worry about their length because that's how they compare each others ability in the bedroom.
guys who have a bit of sense will know that mechanical sex doesnt equal best sex. the best sex is the one where the girl is on cloud 9 and on fire before your overestimated tool goes in!
so basically, forget size; develop a special foreplay move or two likes yours truly :-)