Gunning Fog Index Calculator Calculate the Gunning Fog readability index to measure text complexity.

What Is Gunning Fog Index?

The Gunning Fog Index, developed by Robert Gunning in 1952, estimates years of formal education needed to understand text on first reading. It factors in sentence length and percentage of complex words (3+ syllables). A Fog Index of 12 means a high school senior should understand it. Most magazines score 8-10, newspapers 11-12, and academic journals 15-20. The formula is widely used in corporate communications, journalism, and technical writing. For maximum reach, target a Fog Index of 8-10.

Why Use Gunning Fog Index?

• Identify exact education level needed to comprehend your text
• See which complex words make writing harder to read
• Scores map directly to U.S. grade levels
• Instant results with detailed text statistics
• Favored by journalists and business writers for practical accuracy

Common Use Cases

Business Writing

Keep memos and proposals accessible by targeting a Fog Index of 8-10.

Journalism

Ensure articles meet accessibility standards for the widest audience.

Technical Documentation

Balance technical vocabulary with clear sentence structure.

Marketing Copy

Make sales pages and emails immediately understandable.

Technical Guide

Formula: 0.4 * ((words/sentences) + 100 * (complex_words/words)). A complex word has 3+ syllables, excluding common suffixes like -ing, -ed, -ly, -er, -est, -tion. The tool displays complex words with syllable counts so writers can see which words to replace. Scale: 6 = 6th grade, 12 = high school, 17+ = graduate level.

Tips & Best Practices

• 1
  Target 8-10 for business communications
• 2
  Replace complex words with simpler alternatives
• 3
  Shorten sentences as average sentence length has equal weight
• 4
  Define technical terms on first use
• 5
  Run sections independently since introductions should score lower

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Frequently Asked Questions

Q What is a good Gunning Fog score?

For general audiences, 8-10. Magazines score 8-10, newspapers 11-12, academic journals 15-20.

Q How is a complex word defined?

A word with 3+ syllables, excluding common suffixes that inflate count without adding complexity.

Q Does it work for fiction?

It works but dialogue and narrative style can skew results. Best for informational writing.

Q How many words should I test?

At least 100 words for reliable results.

Q Who uses the Fog Index?

Widely used in journalism, corporate communications, and government agencies.

About This Tool

Gunning Fog Index is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.