Employers, stop asking these interview questions now

Fermi questions are commonly used in interviews but are irrelevant and unfair

Keith McNulty
3 min readMar 10, 2022


Years ago, when I started interviewing with consulting and banking companies for graduate positions, I would be constantly asked Fermi questions.

What is a Fermi question, you might ask? Well here are some examples:

  1. How many $10 bills are in circulation in the US right now?
  2. How many golf balls would it take to fill up a Boeing 777?
  3. How many piano tuners are there in the Chicago area?

Fermi questions are questions that require the estimation of something that is impossible to quantify precisely. They are named after the famous physicist Enrico Fermi, who was known for being able to make physics estimations with almost no data. For example, during the test of the first atomic bomb in the New Mexico desert in 1945, Fermi estimated the amount of energy that was released by sprinkling pieces of paper in the air and observing what happened to them when the shock wave hit.

Even today, these questions are asked in thousands of job interviews. I don’t really know why these questions became so popular. But I do know that they they are irrelevant and unfair.

Why are Fermi questions so popular?

I don’t honestly know why. But my observation is that interviewers who ask Fermi questions usually do it because they enjoy asking them. In fact, I’m pretty sure there are many interviewers who ignore the ‘official’ guidance on interview questions and ask Fermi questions instead. Interviewers who ask these questions are probably highly likely to be men, and highly likely to be of some sort of math-related background.

They probably ask these questions for a number of reasons:

  1. They don’t like following a structured process in interviews and want to run their interview their own way
  2. They like the process of hearing how someone makes estimates with no data
  3. They enjoy seeing how someone reacts to a question that is basically unsolvable to any precise degree
  4. They have their own…



Keith McNulty

LinkedIn Top Voice in Tech. Expert and Author in Applied Mathematics, Data Science, Statistics. Find me on Twitter or keithmcnulty.org