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Guesstimate is a portmanteau of the words guess and estimate, first used by American statisticians in 1934[1] or 1935.[2] It is defined as an estimate made without 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).

The word is sometimes classified as informal English.[5] It may be used in a pejorative sense or as an informal synonym for "estimate".[7][8]

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 golf balls would it take to circle the Earth at the equator ?
Answer: about one billion (109).[9]
  • How many total miles do all Americans drive in a year ?
Answer: about two trillion (2x1012).[10]
  • How much high-level nuclear waste does a 1 GW nuclear power plant produce in a year ?
Answer: about sixty tons.[11]

See alsoEdit


  1. guess Online Etymological Dictionary
  2. 2.0 2.1 guesstimate Unabridged (v 1.1)
  3. guesstimate Merriam-Webster On-line Dictionary
  4. guesstimate MSN Encarta Dictionary
  5. 5.0 5.1 guesstimate American Heritage Dictionary
  6. Compact Oxford English Dictionary guesstimate
  7. "Guesstimate with confidence using confidence intervals" from back cover of Statistics for Dummies
  8. Guesstimate; Grades 4-6 NTTI Lesson Plan
  9. Weinstein & Adam (2008) Problem 3.2
  10. Weinstein & Adam (2008) Problem 5.1
  11. Weinstein & Adam (2008) Problem 10.5
  • Weinstein, Lawrence; Adam, John A. (2008). Guesstimation: Solving the World's Problems on the Back of a Cocktail Napkin, Princeton University Press.
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