Fermi Problem
Back-of-the-Envelope Calculation · Ballpark · Guesstimation
A rough calculation to arrive at a reasonable estimate — unknowns and all — where the result could be considered logically approximate.
Origin
Named for Nobel Prize–winning physicist Enrico Fermi, who was legendary for producing surprisingly accurate estimates from minimal data. While teaching at the University of Chicago in the 1940s — where he also led the team that built the first nuclear reactor for the Manhattan Project — Fermi would challenge students with seemingly impossible questions, most famously: "How many piano tuners are there in Chicago?" At the 1945 Trinity nuclear test, he estimated the bomb's yield by dropping scraps of paper and measuring their displacement.
Everyday Use
There can be so many problems that we encounter on a daily basis that we are reluctant to even address because we assume that we don't have enough information, or couldn't possibly calculate the cost/benefits, for example. Fermi Problem's are good reminders that we often know more than we realize, and taking a stab at calculating something -- even if it's a wild estimate about how long a task will take or how challenging something might be -- can be surprising in getting us in the ballpark of an answer that will be helpful nonetheless.