Skip to content

Fermi Problem

Also Known As...
Back-of-the-Envelope CalculationBallparkGuesstimation
Drake EquationFermi Paradox
Fermi Problem


A rough calculation to arrive at a reasonable estimate — unknowns and all — where the result could be considered logically approximate.


Named for physicist Enrico Fermi's ability to make good approximate calculations with little or no actual data.

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.