Make a Market on Piano Tuners

Question

“Make me a two-sided market on the number of full-time piano tuners working in a city of about nine million people.” You get no data and sixty seconds. Build the estimate out loud, quote a market, and defend your width. What number do you centre on, and how wide do you go before the interviewer can pick you off?

Accepted Answer

This is the canonical estimation market, and the grade is on the chain of reasoning, not the final digit. Build the central estimate. A clean decomposition: nine million people at roughly 2.5 per household gives about 3.6 million households. Say one in fifty owns a piano (around 2%), so about 72,000 pianos. A piano is tuned roughly once a year. One full-time tuner handling about four tunings a day, five days a week, fifty weeks a year does roughly 1,000 tunings annually. So frac72,000 text tunings/year1,000 text tunings/tuner/year approx 72 text tuners. Round to a memorable centre: about 70 tuners, order of magnitude tens, comfortably between 50 and 100. Now quote, which is the part candidates skip. You were asked for a market, not an estimate. Two of your inputs, the piano-ownership rate and the tunings-per-tuner, could each be off by a factor approaching 2, so a defensible quote is something like 55 / 90, bracketing your honest uncertainty. Too tight, say 68 / 72, claims precision a back-of-envelope cannot support, and the interviewer lifts the side you under-thought and bleeds you. Too wide, say 10 / 500, says nothing and reads as no view. The trap to name: quoting a single poin

Make a Market on Piano Tuners

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