Clarifying questions and assumptions:

Piano Tuners - These are people who tune pianos so that the piano produces the right notes. They are called on-demand by individuals with pianos or by places like music schools etc.

Assuming SF population → 1M

Equation:

# of piano tuners in SF = # of users with pianos x avg.piano tuner request frequency

# of users with piano in SF = # of households in SF with piano + # of individuals with pianos

SF is primarily occupied by singles or younger couples who don’t necessarily have a traditional household, Thus assuming 60% of SF is individuals and 40% are households.

400 individuals are part of household → 400K/3 → 133K households

600k individuals

Also, pianos are expensive to buy and maintain, so I am assuming only 50% of households and 25% individuals can actually potentially afford it. Assuming the household has a higher chance of buying it since there are usually 2 or more sources of income.

Potential SF TAM for Pianos

133K x 0.50 → 65K

600K/4 -> 150K

Assuming, 20% of this TAM actually has pianos in San Franciso → 0.2 x (150K+65K)

43K pianos are there in San Francisco.

In general, pianos would require tuning atleast once a quarter and a tuner can tune about 3 pianos per day.

Thus the number of piano tuners needed to meet this demand

43K/(3x90) = 160 piano tuners are in San Franciso

(edited)