Guesstimate is an informal English portmanteau 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 words estimate and guess, guesstimate may be used as a verb or a noun (with the same change in pronunciation as estimate). 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:
Lawrence Weinstein and John Adam's 2009 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 estimating the total number of miles that Americans drive in a year (about 2 trillion)[12] and the amount of high-level nuclear waste that a 1 GW nuclear power plant produces in a year (about 60 tons).[13]