The number of hairdressers depends on three main factors: # of haircuts done per year, time spent per haircut and capacity of each hairdresser.
Number of haircuts: Number of haircuts depends on US population that gets a haircut and how often people get a haircut. I will first tackle the population. Obviously, people aged between 0-10 do not get haircuts. Even if they do, it is exceedingly rare. I assume health expectancy is 80 years and population is evenly distributed among each groups. That means, only 87.5% of the US population gets haircuts. I assume there are 160m males and 160m females in the US. That means, 140m males and 140m females gets haircut each year. I also assume males get a haircut once every month and females get once every three months, which means 12 haircuts per year for males and 4 haircuts per year for females.
This means, total number of haircuts per year is 140m * 12 = 1.68 billion for males and 140m * 4 = 560 million for females.
Time per haircut: I will assume a haircut per male will take 30 minutes while it will take 1 hr for females.
Capacity per hairdresser: I will assume there will be on average four hairdressers per shop and each will work for 40 hours per week. Assuming they will work for 50 weeks per year, capacity of each shop is 8000 worker hour.
Obviously, the number of hairdressers is total hours worked / capacity per hairdresser.
Total hours worked: 1.68 billion * 30 minutes (for males) + 560 million * 1 hr (for females) = 0.84 billion worker hours (for males) + 0.56 billion worker hours (for females) = 1.4 billion worker hours
Capacity per hairdresser: I calculated it above to be 8000 worker hours per year.
Number of hairdressers: 1.4 billion worker hours per year / 8000 worker hours per year = 175,000.
There are approximately 175,000 hairdresser shops, or 700,000 individual hairdressers working in the US.
