Gunning Fog Index

A readability formula that emphasises polysyllabic words; designed for business writing.

The Gunning Fog Index, developed by Robert Gunning, is a grade-level readability formula that weights words of three or more syllables heavily. Formula: 0.4 × (words/sentences + 100 × complex_words/words).

Related terms

  • Readability — How easy a text is to read, typically measured by sentence length and word complexity.
  • SMOG Index — A readability formula calibrated for healthcare and patient-education writing.
  • Flesch–Kincaid Grade Level — A readability formula expressed as a US school grade — grade 8 means an eighth-grader could read it.