It is well known that girls tend to grow faster than boys, especially during puberty. There are several biological and hormonal reasons for this growth difference between the sexes.
Key Facts
- Girls typically begin puberty between ages 8 and 13, while boys begin between ages 9 and 14.
- Girls complete puberty between ages 15 and 17, while boys complete it between ages 16 and 17.
- During puberty, girls experience rapid growth of up to 3.5 inches per year, while boys grow up to 4 inches per year.
- By age 17, the average girl is only two-thirds her adult height, while the average boy is over three-quarters his adult height.
- Estrogen is the main driver of growth in girls, while testosterone is the main driver in boys.
- Girls tend to have an earlier growth spurt and reach their adult height sooner than boys on average.
Timing of Puberty
The most rapid period of growth for both girls and boys occurs during puberty. However, puberty tends to begin earlier for girls. On average, girls begin puberty between the ages of 8 and 13, while for boys it typically begins between ages 9 and 14.
Some key markers of puberty include breast development and menstruation for girls, and testicular enlargement and voice changes for boys. Girls usually start puberty about 1-2 years before boys do.
Age of Onset of Puberty
| Sex | Average Age of Onset |
|---|---|
| Girls | 8-13 years |
| Boys | 9-14 years |
As you can see from the table, girls on average start puberty about 1 year before boys. This head start leads to a growth spurt that also begins earlier for girls.
Timing of Growth Spurts
In addition to beginning puberty at an earlier age, girls also tend to have their pubertal growth spurts about 1-2 years earlier than boys. The peak growth velocity during puberty occurs between about 1-1.5 years after its onset in girls, and about 2-2.5 years after its onset in boys.
In concrete terms, this means girls have their fastest growth spurt between ages 10 and 12, while boys have it between ages 12 and 14. The peak of the growth spurt for girls coincides with the first visible body changes of puberty, while for boys it occurs around 2 years after the first pubertal changes.
Timing of Peak Growth Velocity in Puberty
| Sex | Average Age of Peak Growth Spurt |
|---|---|
| Girls | 10-12 years |
| Boys | 12-14 years |
As illustrated in the table, girls reach their peak growth velocity about 2 years earlier than boys on average. This translates into more rapid growth for girls in the 10-14 year age range.
Rate of Growth During Puberty
In addition to its earlier timing, the pubertal growth spurt also tends to be faster for girls than boys. During their peak growth period, girls may grow at a rate of 3.5 inches per year, while boys growth maxes out at around 4 inches per year.
However, because boys have a later growth spurt, boys continue growing for longer. Many boys keep growing at a rate of 2-3 inches per year until ages 16-17. At the same time, girls have usually stopped growing by age 15.
Therefore, while the growth rate for girls may exceed that of boys during ages 10-14, by the end of puberty boys have typically caught up in total height gained. But girls still reach their adult height about 1-2 years sooner than boys, on average.
Rate of Growth During Peak Pubertal Spurt
| Sex | Rate of Growth Per Year |
|---|---|
| Girls | Up to 3.5 inches |
| Boys | Up to 4 inches |
This table illustrates the faster rate of growth for girls during the peak of their growth spurt. However, boys sustain rapid growth for longer leading to similar total pubertal growth between the sexes.
Total Pubertal Growth
Although girls grow faster than boys in middle puberty, total pubertal growth is similar between girls and boys. Girls grow about 3.5-4 inches per year during their peak growth period from ages 10-12.
Boys, on the other hand, grow more slowly – only about 2-3 inches per year – but sustain this until ages 16-17. This means they continue growing for longer than girls.
Therefore, by the end of puberty, girls have grown about 9-11 inches total, while boys grow about 9-12 inches total. The difference in total growth between the sexes is minor.
Total Height Gained During Puberty
| Sex | Total Pubertal Growth |
|---|---|
| Girls | 9-11 inches |
| Boys | 9-12 inches |
As shown, boys and girls end up gaining a similar number of total inches during puberty once their entire growth periods are taken into account.
Age at Reaching Adult Height
Due to their earlier growth spurt, girls usually reach their adult height at a younger age than boys. On average, girls complete their vertical growth by about age 15 or 16. Boys, on the other hand, may continue growing until age 17 or 18.
By age 17, the average girl has reached over 98% of her adult height. Comparatively, the average boy at 17 has only reached about 93% of his adult height. It takes boys about another 1-2 years to reach their full height potential.
Average Age When Adult Height is Reached
| Sex | Age Adult Height Reached |
|---|---|
| Girls | 15-17 years |
| Boys | 17-18 years |
Due to their earlier pubertal timing, girls reach their maximum height about 2 years earlier than boys, on average.
Factors Influencing Growth Rate Differences
What biological and hormonal factors underlie these differences in growth patterns between girls and boys during puberty?
There are several key contributors:
Estrogen vs Testosterone
The main driver of growth and development in girls during puberty is the hormone estrogen. Estrogen causes maturation of the growth plates leading to their earlier fusion. This speeds up growth in the short term but ultimately cuts it off sooner.
In boys, testosterone is the dominant hormone. Testosterone leads to increasing muscle mass and strength rather than rapid linear growth. Testosterone also matures growth plates later, prolonging the male growth period.
Growth Hormone
In addition to sex steroids, growth hormone levels also spike during puberty and contribute to growth. However, the timing of peak growth hormone secretion aligns with estrogen in girls, contributing to an earlier and faster growth spurt.
In boys, growth hormone peaks later and extends the duration rather than the rate of growth. It declines as testosterone rises, slowing growth as puberty finishes.
Body Composition
Girls accumulate more fat mass during puberty, while boys gain more muscle mass. The earlier acceleration of weight gain and changing body composition in girls contributes to their faster growth rate compared to boys.
Skeletal Maturation
Rising estrogen matures the growth plates of girls leading to earlier fusion. This initially causes faster growth but ultimately cuts off height increase sooner. Later maturation in boys prolongs the open window for growth.
Conclusion
In summary, girls grow faster than boys primarily due to:
- Earlier onset of puberty
- Earlier timing of growth spurt
- Acceleration of growth rate by estrogen
- Earlier maturation of growth plates
The combination of these hormonal and developmental factors lead girls to grow rapidly in their early teen years. However, boys catch up and surpass them in height later on due to their prolonged growth period.
Understanding the differences in growth patterns between girls and boys helps explain the observation that girls grow faster than boys during puberty and reach their adult height sooner. While girls sprint ahead initially, boys eventually catch up over their longer marathon of growth.