Jun 18

After helping you to calculate the SMOG index of a text, Joe’s Web Tools explains you the SMOG readability formula, which is used to assess the years of formal education a writer would need to understand a text.

SMOG is an acronym for Simple Measure of Gobbledygook. The SMOG Index was an attempt by G. Harry McLaughlin in 1969 to improve on the Gunning-Fog Index. It was an easier formula devised to give a more accurate scores. The formula offers a 0.985 correlation with a standard error of 1.5159 grades vis-à-vis grades of readers who had complete understanding of test materials. The formula entails counting the words of three or more syllables in three-sentence samples, calculating the square root of the answer, (rounded off to the nearest perfect square) and adding the constant 3.1291.

To calculate the SMOG, first select 10 sentences from the start, the middle, and the end of the text. Count the words of three or more syllables. Now use the following formula:

SMOG Index Formula

Points that should be kept in mind when counting words:

  • Hyphenated words are considered as one word
  • Proper nouns are counted too
  • Abbreviations are de-abbreviated before counting to check whether they are multi-syllabic

Documents which have less than 30 sentences follow this formula:

  • All the multi-syllable words are counted in the text, as are the number of sentences.
  • The average number of multi-syllabic words is calculated by dividing the total number of multi-syllabic words by the total number of sentences.
  • This average is multiplied by the number of sentences it is falling short of 30.
  • The figure is added to the total number of multi-syllabic words.
  • Now the square root is calculated and a constant of 3 is added.

The SMOG formula is used in health-related documents, and helps ensure that they are understood. SMOG applied materials make good teaching aids for undergraduate and graduate health education students and help disseminate health information better. The SMOG readability test that we have here at Joe’s Web Tools can be applied to various documents online.