''Guesstimate'' is an informal

English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ...

portmanteau A portmanteau word, or portmanteau (, ) is a blend of wordsguess A guess (or an act of guessing) is a swift conclusion drawn from data directly at hand, and held as probable or tentative, while the person making the guess (the guesser) admittedly lacks material for a greater degree of certainty. A guess is als ...

'' and ''

estimate Estimation (or estimating) is the process of finding an estimate or approximation, which is a value that is usable for some purpose even if input data may be incomplete, uncertain, or unstable. The value is nonetheless usable because it is de ...

'', first used by American

statistician A statistician is a person who works with theoretical or applied statistics. The profession exists in both the private and public sectors. It is common to combine statistical knowledge with expertise in other subjects, and statisticians may w ...

s in 1934 or 1935.''guesstimate''
Dictionary.com Unabridged (v 1.1) It is defined as an estimate made without using adequate or complete information, or, more strongly, as an estimate arrived at by

guess A guess (or an act of guessing) is a swift conclusion drawn from data directly at hand, and held as probable or tentative, while the person making the guess (the guesser) admittedly lacks material for a greater degree of certainty. A guess is als ...

work or

conjecture In mathematics, a conjecture is a conclusion or a proposition that is proffered on a tentative basis without proof. Some conjectures, such as the Riemann hypothesis (still a conjecture) or Fermat's Last Theorem (a conjecture until proven in ...

.''guesstimate''
American Heritage Dictionary Like the words estimate and guess, guesstimate may be used as a verb or a noun (with the same change in

pronunciation Pronunciation is the way in which a word or a language is spoken. This may refer to generally agreed-upon sequences of sounds used in speaking a given word or language in a specific dialect ("correct pronunciation") or simply the way a particular ...

as estimate). A guesstimate may be a first rough

approximation An approximation is anything that is intentionally similar but not exactly equal to something else. Etymology and usage The word ''approximation'' is derived from Latin ''approximatus'', from ''proximus'' meaning ''very near'' and the prefix ' ...

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 A pejorative or slur is a word or grammatical form expressing a negative or a disrespectful connotation, a low opinion, or a lack of respect toward someone or something. It is also used to express criticism, hostility, or disregard. Sometimes, a ...

sense if information for a better estimate is available but ignored. Guesstimation techniques are used: *in

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...

, where the use of guesstimation techniques to solve Fermi problems is taught as a useful skill to science students; *in

cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosopher ...

, where the

Drake equation The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy. The equation was formulated in 1961 by Frank Drake, not for purposes of quantifying ...

is a well-known guesstimation method; *in

economics Economics () is the social science that studies the production, distribution, and consumption of goods and services. Economics focuses on the behaviour and interactions of economic agents and how economies work. Microeconomics anal ...

, where economic forecasts and statistics are often based on guesstimates; and *in

software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' ...

, where new development of features and release timelines are based on effort guesstimates of tasks. 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 Old Dominion University (Old Dominion or ODU) is a public research university in Norfolk, Virginia. It was established in 1930 as the Norfolk Division of the College of William & Mary and is now one of the largest universities in Virginia w ...

, 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) and the amount of high-level nuclear waste that a 1 GW nuclear power plant produces in a year (about 60 tons).Weinstein & Adam (2008) Problem 10.5 __NOTOC__

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The Fermi Project: Collection of guesstimates for practice
{{Webarchive, url=https://web.archive.org/web/20200817075234/https://www.fermiproblems.in/ , date=2020-08-17 American slang Informal estimation Measurement

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