Guesstimate

Guesstimate is an informal English contraction of guess and estimate, first used by American statisticians in 1934^[1] or 1935.^[2] It is defined as an estimate made without using adequate or complete information,^[3][4] or, more strongly, as an estimate arrived at by guesswork or conjecture.^[2][5][6] Like the word estimate, guesstimate may be used as a verb or a noun (with the same change in pronunciation). A guesstimate may be a first rough approximation pending a more accurate estimate, or it may be an educated guess at something for which no better information will become available.

The word may be used in a pejorative sense if information for a better estimate is available but ignored.^[7][8]

Guesstimation techniques are used:

• in physics, where the use of guesstimation techniques to solve Fermi problems is taught as a useful skill to science students.^[9]
• in cosmology, where the Drake equation is a well-known guesstimation method.^[10]
• in economics, where economic forecasts and statistics are often based on guesstimates.^[11]

Lawrence Weinstein and John Adam's book Guesstimation: Solving the World's Problems on the Back of a Cocktail Napkin, based on the course "Physics on the Back of an Envelope" at Old Dominion University, promotes guesstimation techniques as a useful life skill. It includes many worked examples of guesstimation, including the following problems:

• How many total miles do all Americans drive in a year?

Answer: about two trillion (2x10¹²).^[12]

• How much high-level nuclear waste does a 1 GW nuclear power plant produce in a year?

Answer: about sixty tons.^[13]

See also

• Ballpark estimate
• Back-of-the-envelope calculation

References

• Weinstein, Lawrence; Adam, John A. (2008). Guesstimation: Solving the World's Problems on the Back of a Cocktail Napkin. Princeton University Press. ISBN 9780691129495.