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Flesch-Kincaid & Gunning Fog Readability Score Calculator

Analyze text readability instantly using Flesch Reading Ease, Flesch-Kincaid Grade Level, and Gunning Fog Index scores for free.

Formula Verified by Dr. Arthur Pendelton, PhD

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

Text to Analyze

Results

Flesch Reading Ease

17.7

Flesch-Kincaid Grade LevelGrade 14.1

Gunning Fog Index18.7

Sentences: 2

Words: 27

Syllables: 56

Complex Words (3+ syllables): 9

Tip

Save this calculator to audit copy readability, align content with target audiences, and optimize text for search engine guidelines.

Formula

Readability Index Formulas

Flesch Ease = 206.835 - 1.015 × (Words/Sentences) - 84.6 × (Syllables/Words) 
Flesch-Kincaid Grade = 0.39 × (Words/Sentences) + 11.8 × (Syllables/Words) - 15.59

Uses syllable counters and sentence boundary parsing to estimate linguistic readability standards.

Step by step

How the calculation works

1Type or paste your text into the entry box.
2Review the real-time Flesch Reading Ease score (higher is easier) and grade level (lower is more accessible).
3Optimize text by breaking up long sentences and replacing high-syllable vocabulary with simple alternatives.

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Guide

Understanding Calculator Formulas: How DTC Turns Inputs into Results

Understand how Do The Calculation formulas are presented, what the explanation blocks mean, and how to verify calculator logic before using a result in a real decision.

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How to understand and use this calculator

Flesch Reading Ease Formula: Syllables, Words, and Sentence Ratios

The Flesch Reading Ease index is one of the most widely used readability formulas. It measures how easy a text is to read based on average sentence length (words per sentence) and average word length (syllables per word). The mathematical formula is:

F.R.E. = 206.835 - 1.015 (words/sentences) - 84.6 (syllables/words)

Scores range from 0 to 100. A score between 90 and 100 indicates fifth-grade reading ease (very easy), 60 to 70 indicates standard eighth-to-ninth-grade level, and 0 to 30 indicates university graduate level (extremely difficult). Sorter sentences and fewer syllables yield higher scores.

Flesch-Kincaid Grade Level Formula: Correlating Scores with US School Grades

The Flesch-Kincaid Grade Level formula translates the Reading Ease score directly into a US school grade level, making it easier for educators and writers to target specific student audiences. The mathematical formula is:

F.K.G.L. = 0.39 (words/sentences) + 11.8 (syllables/words) - 15.59

For example, a score of 8.2 means the text is appropriate for an eighth-grade student (approx. 13-14 years old). This index is widely used by government agencies, military organizations, and publishers to standardize document clarity.

The Gunning Fog Index: Factoring in Complex Words

Developed by Robert Gunning in 1952, the Gunning Fog Index is another readability formula that estimates the years of formal education required to understand a text. In addition to sentence length, Gunning Fog uses the percentage of "complex words" (words containing three or more syllables). The formula is:

G.F.I. = 0.4 × [ (words/sentences) + 100 ((complex words)/words) ]

We exclude proper nouns, familiar jargon, and three-syllable verbs ending in standard suffixes (like -es, -ed, or -ing) from the complex word count. A Gunning Fog score of 7-8 is standard for popular novels, while scores above 12 indicate academic or legal text.

Linguistic Readability in SEO: Google’s Helpful Content Guidelines

Readability metrics are highly relevant for digital publishers. Google’s Helpful Content updates prioritize people-first content that is clear, accessible, and structured for easy scanning. Writing clear sentences with high readability scores improves user engagement, reduces bounce rates, and increases time-on-page.

To analyze your text statistics in detail, you can combine this readability analyzer with our word counter which counts characters, paragraphs, and reading times, or use the AI token estimator to estimate text size for LLM prompts.

How to Use This Readability Score Calculator

Paste or type any text into the analysis box. The calculator counts sentences, words, and syllables in real time and computes three scores at once: Flesch Reading Ease, Flesch-Kincaid Grade Level, and the Gunning Fog Index.

Use the word complexity breakdown chart to see what share of your text is made up of complex (3+ syllable) words, and revise toward shorter sentences and simpler vocabulary to raise the Reading Ease score.

Worked Example: Scoring the Default Sample Paragraph

The calculator's default two-sentence, 27-word sample — about readability formulas themselves — produces a Flesch Reading Ease score of about 17.7 (university graduate level, quite difficult), a Flesch-Kincaid Grade of about 14.1, and a Gunning Fog Index of about 18.7.

This is expected: the sample text is dense with multi-syllable technical words like "mathematical," "algorithms," and "readability," which is exactly the kind of vocabulary all three formulas penalize.

Related Calculators

This analyzer is part of a Text Encoding Tools cluster. Pair it with the Word Counter Calculator for character and reading-time stats, or the Text Case Converter and Text Diff Comparison Tool for other writing workflows.

Related concepts

Linguistic Density

The ratio of content words (nouns, verbs, adjectives) to grammatical function words in a text.

Flesch Reading Ease

A readability scale from 0 to 100 where higher scores indicate text that is easier to read.

Gunning Fog Index

A readability formula designed to estimate the formal US education years required to read a document.

Frequently Asked Questions

What is a readability score?+

A readability score is a computer-calculated index that estimates the reading ease or grade level of a text based on sentence structure, word lengths, and syllable counts.

What is a good Flesch Reading Ease score?+

A score between 60 and 70 is considered standard, representing an 8th-to-9th-grade reading level, which is easily understood by the average adult.

How does Gunning Fog calculate complex words?+

Complex words are defined as words containing three or more syllables, excluding proper nouns, compound words, and verbs ending in standard suffixes like -ed, -es, or -ing.

How can I improve my readability score?+

To improve readability, shorten your sentences, break up complex paragraphs, and replace long, multi-syllable words with simpler synonyms.

Why do readability scores exclude proper nouns?+

Proper nouns (like names of people, cities, or brands) can contain many syllables but do not increase reading difficulty in the same way as complex vocabulary.

What reading level is standard for the web?+

An 8th-grade reading level (Flesch-Kincaid Grade 8 or Flesch Reading Ease 60–70) is the standard recommendation for public web content to ensure broad accessibility.

Are readability scores used by Google search?+

While Google does not use readability formulas as a direct ranking factor, clear content improves user experience and time-on-page, which positively impacts SEO.

What is the Flesch-Kincaid Grade Level formula?+

Flesch-Kincaid Grade Level = 0.39 * (words/sentences) + 11.8 * (syllables/words) - 15.59.

Can readability formulas analyze poetry?+

No, readability formulas rely on grammatical sentence structures and average word counts, making them inaccurate for poetry or highly formatted text.

How do you count syllables in a word programmatically?+

Syllables are estimated using regular expressions that count vowel groups while adjusting for silent vowels (like trailing "e"), prefixes, and suffixes.

How to understand and use this calculator

Flesch Reading Ease Formula: Syllables, Words, and Sentence Ratios

F.R.E. = 206.835 - 1.015 (words/sentences) - 84.6 (syllables/words)

Flesch-Kincaid Grade Level Formula: Correlating Scores with US School Grades

F.K.G.L. = 0.39 (words/sentences) + 11.8 (syllables/words) - 15.59

The Gunning Fog Index: Factoring in Complex Words

G.F.I. = 0.4 × [ (words/sentences) + 100 ((complex words)/words) ]

Linguistic Readability in SEO: Google’s Helpful Content Guidelines

How to Use This Readability Score Calculator

Worked Example: Scoring the Default Sample Paragraph

Related Calculators

Related concepts

Linguistic Density

The ratio of content words (nouns, verbs, adjectives) to grammatical function words in a text.

Flesch Reading Ease

A readability scale from 0 to 100 where higher scores indicate text that is easier to read.

Gunning Fog Index

A readability formula designed to estimate the formal US education years required to read a document.

Frequently Asked Questions

What is a readability score?+

A readability score is a computer-calculated index that estimates the reading ease or grade level of a text based on sentence structure, word lengths, and syllable counts.

What is a good Flesch Reading Ease score?+

A score between 60 and 70 is considered standard, representing an 8th-to-9th-grade reading level, which is easily understood by the average adult.

How does Gunning Fog calculate complex words?+

Complex words are defined as words containing three or more syllables, excluding proper nouns, compound words, and verbs ending in standard suffixes like -ed, -es, or -ing.

How can I improve my readability score?+

To improve readability, shorten your sentences, break up complex paragraphs, and replace long, multi-syllable words with simpler synonyms.

Why do readability scores exclude proper nouns?+

Proper nouns (like names of people, cities, or brands) can contain many syllables but do not increase reading difficulty in the same way as complex vocabulary.

What reading level is standard for the web?+

An 8th-grade reading level (Flesch-Kincaid Grade 8 or Flesch Reading Ease 60–70) is the standard recommendation for public web content to ensure broad accessibility.

Are readability scores used by Google search?+

While Google does not use readability formulas as a direct ranking factor, clear content improves user experience and time-on-page, which positively impacts SEO.

What is the Flesch-Kincaid Grade Level formula?+

Flesch-Kincaid Grade Level = 0.39 * (words/sentences) + 11.8 * (syllables/words) - 15.59.

Can readability formulas analyze poetry?+

No, readability formulas rely on grammatical sentence structures and average word counts, making them inaccurate for poetry or highly formatted text.

How do you count syllables in a word programmatically?+

Syllables are estimated using regular expressions that count vowel groups while adjusting for silent vowels (like trailing "e"), prefixes, and suffixes.

Flesch-Kincaid & Gunning Fog Readability Score Calculator

Inputs

Results

Readability Index Formulas

How the calculation works

Learn more about this calculation

Understanding Calculator Formulas: How DTC Turns Inputs into Results

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Flesch-Kincaid & Gunning Fog Readability Score Calculator

Inputs

Results

Key output metrics

Readability Index Comparison

Word Complexity Breakdown

How to understand and use this calculator

Flesch Reading Ease Formula: Syllables, Words, and Sentence Ratios

Flesch-Kincaid Grade Level Formula: Correlating Scores with US School Grades

The Gunning Fog Index: Factoring in Complex Words

Linguistic Readability in SEO: Google’s Helpful Content Guidelines

How to Use This Readability Score Calculator

Worked Example: Scoring the Default Sample Paragraph

Related Calculators

Related concepts

Frequently Asked Questions

Readability Index Formulas

How the calculation works

Learn more about this calculation

Understanding Calculator Formulas: How DTC Turns Inputs into Results

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Key output metrics

Readability Index Comparison

Word Complexity Breakdown

How to understand and use this calculator

Flesch Reading Ease Formula: Syllables, Words, and Sentence Ratios

Flesch-Kincaid Grade Level Formula: Correlating Scores with US School Grades

The Gunning Fog Index: Factoring in Complex Words

Linguistic Readability in SEO: Google’s Helpful Content Guidelines

How to Use This Readability Score Calculator

Worked Example: Scoring the Default Sample Paragraph

Related Calculators

Related concepts

Frequently Asked Questions