I have thoroughly enjoyed reading through the responses in the 5+ years since I posted this question.
I think it's time to update my own number, since I have had recent medical issues that have affected my size.
I was always a solid 5.75" but, unless my eyes were playing tricks on me, I noticed an increase to 6" during Covid-19, a time spent doing a lot of masturbating. I was more than OK with 5.75. The extra quarter-inch was icing on the cock.
In the spring of this year I had a prostatectomy. Hard to tell how it affected my erect size because following the surgery I was impotent. After a number of failed treatments I just last week underwent an implant of an inflatable penile prosthesis which, once I'm healed, will produce a rigid erection. Not sure of the final size yet, but while I'm healing, the apparatus is in semi-inflated status 24/7. When I stand, it points straight out at a perpendicular angle. While it's supposedly only semi-inflated, it seems pretty full. Not sure but I think it's at its maximum length. I think the only difference will be when it's fully inflated, it will point up instead of out. The measurement I took of it in its current state is between 4.75" and 5". Not what I wanted, but that's mainly ego speaking. My wife isn't bothered by the reduction.
I can tell you, while I was unconscious, they measured me so they would know what size cylinders to implant in my penis. From the post-op notes:
"The measuring tool revealed measurements of 11 cm proximal and 12 cm distal for final measurements of 23 cm bilaterally"
One factor to consider is I'm not sure how much of my penis they measured. Was it to the tip or to the corona? And how much of the two cylinders are in my pelvis, not inside the penile shaft?
One final note. While I'm disappointed to be smaller. I'm very, very happy to one day again be able to make love to my wife with a fully erect member!