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SMOG (Simple Measure of Gobbledygook) is a readability formula that estimates the years of education needed to completely understand a piece of writing. SMOG is widely used, particularly for checking health messages.[1] [2] The SMOG formula yields a 0.985 correlation with a standard error of 1.5159 grades with the grades of readers who had 100% comprehension of test materials.[3]

SMOG was published by G. Harry McLaughlin in 1969 as a more accurate and more easily calculated substitute for the Gunning-Fog Index. To make calculating a text's readability as simple as possible an approximate formula was also given — count the words of three or more syllables in three 10-sentence samples, estimate the count's square root (from the nearest perfect square), and add 3.

Applying SMOG to other languages[4] lacks statistical validity.


To calculate SMOG

  1. Count a number of sentences (at least: 10 from the start of a text, 10 from the middle, and 10 from the end).
  2. In those sentences, count the polysyllables (words of 3 or more syllables).
  3. Calculate using
\mbox{grade} = 1.0430 \sqrt{ 30\times\frac{\mbox{number of polysyllables}}{\mbox{number of sentences}} } + 3.1291

A version is also given which is more easily used for mental math and is sometimes known as the SMOG Index:

  1. Count the number of polysyllabic words, excluding proper nouns, in a sample of thirty sentences.
  2. Take the square root of the nearest perfect square
  3. Add 3

See also Edit


  1. Hedman, Amy S. (January 2008). Using the SMOG formula to revise a health-related document. American Journal of Health Education 39 (1): 61-64.
  2. Ley, P., T. Florio (February 1996). The use of readability formulas in health care. Psychology, Health & Medicine 1 (1): 7–28.
  3. McLaughlin, G. Harry (May 1969). SMOG Grading — a New Readability Formula. Journal of Reading 12 (8): 639–646.
  4. Contreras, A., Garcia-alonso, R.; Echenique, M.; Daye-contreras, F. (1999). The SOL Formulas for Converting SMOG Readability Scores Between Health Education Materials Written in Spanish, English, and French. Journal of Health Communication 4 (1): 21–29.

External links Edit

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