Thank you for your query at AskTheDoctor.com
I understand your concern.
Normal size of an erect penis ranges from 4" to 7 ". If your erect penile size falls in that range, then there is nothing to be worried about. A lot of males are worried their size is inadequate and do not feel confident while having sex because of the same reason. In reality, only the outer 1/3 rd of the female vagina has stimulatory receptors. And for them to enjoy sex, the erect penis need not be more than 3-4 ".
If your penis size is smaller than that, you need to get it examined by your physician and get your serum testosterone evaluated. Low testosterone levels can lead to reduced penile length and correcting the level with external supplementation improves the penile length. Other methods such as jelqing can increase the size by a few centimeters.
Hope this was helpful,
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