Written and reviewed by Dr. Toni Kim
Board Certified Pediatric Endocrinologist
Founder, Life Pediatric Endocrinology
If you were told your son has a testicular volume of 4 mL, you may be wondering whether puberty has officially started.
The short answer is yes.
A testicular volume of 4 mL is considered the earliest clinical sign of puberty in boys.
But here is what often gets missed:
The start of puberty is not just a milestone. It is the start of a biological clock.
Puberty begins when the brain increases signaling through the hypothalamic pituitary gonadal axis.
This stimulates the testes to enlarge.
Typical volumes:
Testicular enlargement usually occurs before voice change, muscle growth, or visible height acceleration.
It is the first measurable sign.
When testicular volume reaches 4 mL, testosterone production begins rising.
Testosterone then:
Here is the critical concept:
Once puberty begins, skeletal maturation accelerates.
Growth plates do not close immediately.
But they do begin progressing toward closure.
Puberty does not just create growth.
It also starts limiting the time available for growth.
You can read more about how to keep growth plates open in this article by Dr. Toni Km
Puberty in boys typically begins between ages 9 and 14.
If 4 mL occurs at age 10 or 11, that is generally within normal range.
If it occurs before age 9, evaluation is appropriate.
However:
Normal timing does not guarantee normal progression.
What determines long term height outcome is not simply when puberty starts.
It is how quickly it progresses.
After reaching 4 mL:
The major pubertal growth spurt typically occurs later, around Tanner stage 3 to 4.
But the hormonal cascade has already begun.
This is why tracking matters from the beginning.
Many boys are told:
He is just starting puberty. That is normal.
That may be true.
But here is what should be clarified before offering reassurance:
If those questions are not answered, reassurance may be premature.
Puberty is not a single visit diagnosis. It is a trajectory that must be tracked.
Further evaluation is appropriate if:
Most boys with 4 mL testicular volume are entering normal puberty.
But a small percentage may not be.
Early identification provides more options.
Waiting reduces flexibility.
Here is the protective truth:
Once puberty progresses, the growth window narrows gradually and permanently.
If progression is rapid and bone age advances quickly, final adult height can be affected.
This does not mean intervention is always needed.
But it does mean monitoring must be intentional.
If pubertal progression has not been documented carefully over time, it has not truly been evaluated.
Yes. Testicular volume of 4 mL is considered the onset of puberty in boys.
Not immediately. The major growth spurt occurs later.
Not always. Testing depends on age and growth pattern.
Yes, particularly if progression is rapid.
Typically every 3 to 6 months during early puberty.
If your son has reached a testicular volume of 4 mL, this is the beginning of an important developmental phase.
At Life Pediatric Endocrinology, we calculate growth velocity, assess skeletal maturity, and monitor pubertal progression before offering reassurance.
We serve families across the United States, with offices in Georgia, Tennessee, Texas, and California, and offer nationwide virtual consultations. Schedule a consultation to learn more about your child's puberty stage and overall development
When puberty begins, precision is not optional.