The phrase back-of-the-envelope refers to rough calculations that, while not rigorous, test or support a point. They are far more than a guess but far less than a proof. The phrase is generally used in mathematics and physics, and can also be found in many engineering fields.

The phrase is derived from the practice of quickly jotting down calculations on the piece of paper nearest to hand, which in pre-email days often meant the back of an envelope.

Note that the term is an analogy; back-of-the-envelope calculations need not be performed on an envelope, but could be performed on a computer or other device. The defining factor is the use of simplified, scaled-down models.

External links

Praveen's Back of the Envelope page, a project at Northwestern University attempting to automate the process (http://www.cs.northwestern.edu/~paritosh/research/intro/)