How many inches (erect) is considered too small of a penis?

Penis size: A study from california found that the average erect penis is 5.6 inches in length. A condition called microphallus (small penis) is very rare and usually discovered in childhood. The variability of penis size is great; don't worry about it you have a 99%chance you are normal.

If too small for sex: Probably 3 inches or less for an adult male. Obesity can be a problem for men with already small penises. Also for their partners.