I'm pretty sure your size is gonna get bigger if you do have an implant. You'll definitely become a shower instead of a grower. Doctor will measure your total length and it'll be over 4-1/4” since it needs to go behind your pubic bone also. I replied with this comment to a post a while back. Let me copy/paste it here:
What you can expect is you would become a shower. To the best of my knowledge (meaning I'm confident I'm correct but I'm sometimes an idiot) is that the size of the implant in cms will correspond to the size of your erect penis now. Meaning, the implant size would have nothing to do with your current flaccid size but will have everything to do with your penis at its full erection size. I learned this by asking my doctor about how they measured my penis:
Hi, I talked to my patient liaison from Boston Scientific and she explained to me (I think) that for my penile implant surgery you measure my penis size as it was necessary for the size of the implant. So, what is it? I imagine it's a sensitive question for a lot of men, but if its in the records l'd like to hear it. Thanks
His response:
During surgery your total penile length measured 24 cm which is about 9-1/2 inches. That is the total length including the part of the shaft goes up underneath your pubic bone in front.
I asked for some clarification because I obviously don't have a 24cm (9.44") dick, and he responded:
Your penis actually extends beyond what you can easily see even with it stretched out completely. There is a portion that goes underneath your pubic bone and in fact is attached to the pubic bone to help support the penis. We would put in the implant, we have to include that area in the total length of the implant. So while you are asleep we are able to place the measuring device down into that part in order to get the total length of the penis. So the length of the implant is longer than what you can actually see. In fact you may be able to even feel the implant in your crotch area where the cylinders go back along the penile corpora that far back. I know that is a confusing explanation but I hope it accounts for your measurements in comparison to what measurements we got in the operating room.
The way I interpret this is they basically measured my stretched flaccid, which was 8.75" pre-surgery. My normal flaccid size was about ~4.8" pre-surgery, but that isn't relevant to the implant procedure. My flaccid size now increased from ~4.8" to a bit above 7" bone pressed.
What I am also fairly confident that you can expect is that your implant at full inflation will result in an erection
longer than 4".
I really liked this video I saw yesterday explaining how the AMS 700 LGX works which helped me reach this conclusion about what you can expect:
https://www.youtube.com/watch?v=Z24GRfTGPTACurrently my stretched flaccid is a bit above 9", and lately my erect size has been rising slow and steady. For the first month I regained size fast - after surgery but before my implant was activated I measured at 6.5". It gets activated and after another month with exercises it's back to 8". From there it's been increasing slow and steadily. Different days and different pumping results have not been consistent, but I'm currently getting measurements of ~8.5" or a bit longer. It's my belief I will grow larger than that, but it'll take time. Fortunately there are medical studies reporting men regaining/gaining size up to 18 months post-implant.