My 11 year old son is asking me if a 4 in. penis (erect) normal?

Penis Development: Penis length in a prepubertal male varies greatly. At puberty (starts typically between ages 9-14), the genital area will grow hair, the testicles will enlarge and the penis will grow in length and width. By the end of the puberty cycle in males, the average penis size will be 5.16 inches. Of course, variability is found in each individual. There will be men with larger or smaller penises.

"Hard" to say: Jyst a little humor there!There really are not good data for what a normal range is for erect penis at age 11. I would reassure him that at his age some boys have started growth of penis, but many have not yet. He still has years to grow yet, so reassurance is your best option at this age.

Yes: 11-y-o boy is at Tanner stage II, and lengthening of penis barely started. It is very likely that his penile length outreach an average 5.1 inches at age 15.