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.

$$1.0430\sqrt{ \text{number of polysyllables} \times\frac{30}{\text{number of sentences}}} + 3.1291$$

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.