SMOG Index

The SMOG index ("Simple Measure of Gobbledygook") was developed by G. Harry McLaughlin in 1969. SMOG provides an estimate for years of education needed to understand a text. The SMOG formula, provided below, uses a count of polysyllables, meaning words with three or more syllables. Note that SMOG is only valid if there are at least 30 sentences in the text.

SMOG index scores correspond roughly to US grade levels, meaning that a higher index indicates a more difficult text. For example, an index of 6 corresponds to 6th grade and an index of 15 corresponds to a university junior.