Gunning Fog Index (GFI)

The Gunning Fog Index (GFI) provides a measure of reading difficulty based on school grade levels. It calculates a grade-level equivalent score by counting words of three or more syllables, number of sentences, and average number of words in sentences.

Formula:

Fog Index = 0.4 x words/sentence + 100 x [(words >= 3 syllables)/words]