The number of hairs per head depends on the hair density (hairs/scalp area).
The hair density varies by ethnicity, age, scalp region and scalp conditions such as male and female pattern alopecia. Considering most of the scientific data available, there’s a consensus that, in average, a head has around 100,000 hairs.
Some scientific studies suggest that both Asian and African groups have similar hair density and that is significantly lower than for Caucasians. Based on the differences on hair density, it is suggested approximately 81,000–121,000 hairs on the scalp for female Caucasians, 89,000 scalp hairs for Asian females; and 81,500 scalp hairs for African females, considering individuals between 18–35 years old. The study was done with individuals not suffering of hair alopecia and didn’t identify differences per gender (Diversity of hair growth profiles.).