How many piano tuners work in Chicago?

Fermi's own question, worked from both ends (how many pianos need tuning, how many one tuner can handle) and then asking sensitivity() which guess to research next.

Demand: pianos that need tuning

The Chicago metro area has about 9.4 million people, in households of about 2.5.

people = 9.2 to 9.6 million
household_size = 2.4 to 2.7
households = people / household_size

households =3.69 × 10⁶ [3.47 × 10⁶, 3.93 × 10⁶]

What fraction of homes have a piano? Think of the homes you've been in: it's more than one in a hundred and fewer than one in ten. Schools, churches, bars and concert halls add more, perhaps a quarter again as many.

have_piano = 3% to 10%
institutional = 1.1 to 1.5
pianos = households * have_piano * institutional

pianos =260000 [140000, 480000]

Piano technicians recommend tuning once or twice a year. Many home pianos go years without one, though, while a concert piano gets tuned before every performance. Averaged over all of them, somewhere between once every three years and a bit more than once a year.

tunings = 0.3 to 1.5 per year
demand = pianos * tunings

demand =200000 [60000, 500000] year⁻¹ {frequency}

Supply: what one tuner can do

A tuning takes one to two hours, and getting to the next client takes another half hour to an hour. A self-employed tuner spends part of each day on scheduling, invoicing and repairs rather than with clients, and takes some weeks off.

tuning_time = 1 to 2 hour
travel = 0.5 to 1 hour
client_hours = 6 to 8 hour/day
working_days = 200 to 240 day/year
capacity = client_hours * working_days / (tuning_time + travel) as 1/year

capacity =700 [510, 950] year⁻¹ {frequency}

Hours per day times days per year, divided by hours per tuning, leaves tunings per year: about 700 [510, 950] year⁻¹.

tuners = demand / capacity

tuners =300 [90, 700]

Tunings per year divided by tunings per tuner-year leaves a count of tuners, about 300 [90, 700]. The range is wide: nearly a factor of eight from end to end.

Where the uncertainty comes from

Most of that spread comes from one or two guesses. sensitivity ranks the inputs by how much of the answer's variance each explains.

sensitivity(tuners)

300 [90, 700]

Sensitivity of tuners (share of variance):
  tunings      +  54%  ███████████
  have_piano   +  30%  ██████
  tuning_time  +   5%  █
  6 others        12%  ██

Population and household size barely matter; they're the inputs we know well. How often pianos get tuned and how many homes have one carry nearly everything. To tighten the estimate, call a piano tuner and ask how often their clients book, rather than refining the census figures.

How close is it?

The Bureau of Labor Statistics counts 150 musical instrument repairers and tuners in the Chicago–Naperville–Elgin metro area (OEWS, May 2025). That figure counts every instrument, not just pianos, and leaves out the self-employed, which many piano tuners are. Both effects are a factor of two or so, in opposite directions, so the estimate is consistent.