A Fermi estimate or back-of-the-envelope calculation (BOTEC) is a rough calculation which aims to be right within about an order of magnitude, prioritizing getting a good enough to be useful answer without putting large amounts of thought and research in rather than being extremely accurate. Open Philanthropy routinely uses BOTECs for impact assessment and cause prioritization.

Further reading

Berger, Alexander (2014) Alexander’s back of the envelope “importance” calculations, GiveWell.

Muehlhauser, Luke (2013) Fermi estimates, LessWrong, April 11....

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