Gunning Fog Index
Estimate the readability of text with the Gunning Fog Index.
About Gunning Fog Index
The Fog Index combines average sentence length with the share of multi-syllable words, returning a rough school grade for the passage. A score below 8 is conversational while above 12 grows demanding. A high fog index flags prose that packs too many long words and long sentences, which drives readers away from dense documents.
Formula
Gunning Fog Index
Fog = 0.4 x (words/sentences + 100 x complex words/words)
- complex words
- Words with three or more syllables
Worked example
With the default values below, Gunning Fog Index returns Fog Index of 12.7. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Wordsminimum 1
- 150
- Sentencesminimum 1
- 10
- Complex wordsminimum 0
- 25
Results
- Fog Index
- 12.7
- Fog Band
- College reading level
- Share Complex Words
- 16.7%
Step by step
- 1Values used
- 2Gunning Fog Index
- 3Fog Index= 12.7
- 4Fog Band= College reading level
- 5Share Complex Words= 16.7
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Gunning Fog Index calculated?
Fog = 0.4 x (words/sentences + 100 x complex words/words) The Fog Index combines average sentence length with the share of multi-syllable words, returning a rough school grade for the passage. A score below 8 is conversational while above 12 grows demanding.
Why does Gunning Fog Index matter?
A high fog index flags prose that packs too many long words and long sentences, which drives readers away from dense documents.
What values do I need to enter?
This calculator takes 3 inputs: Words, Sentences, Complex words. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.