Free Online Readability Checker
Check your text's readability using 6 industry-standard formulas. Get Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau, ARI scores, and a full grade-level breakdown.
The most widely used readability formula. Scores 60–70 are ideal for general audiences. Below 30 is very difficult; above 80 is very easy.
Converts the Flesch score to a US school grade level. A score of 8 means 8th graders can understand the text. Used by the US Department of Defense.
Estimates years of formal education needed to understand the text on first reading. Under 8 is accessible; above 12 is difficult for most readers.
Uses characters per word instead of syllables — more consistent for digital text. Developed in 1975 and outputs a US grade level. Reliable for automated analysis.
Simple Measure of Gobbledygook. Requires 30+ sentences for accuracy. Preferred by healthcare and government writers for its proven predictive accuracy.
Developed by the US Air Force to test technical manuals. Uses characters per word and words per sentence. Highly accurate for technical and professional writing.
What is a Readability Checker?
A readability checker is a tool that measures how easy or difficult your text is to read. Our free online readability checker is the most comprehensive available — it calculates six different readability scores simultaneously, giving you a complete picture of your content's reading level.
The 6 readability formulas explained:
1. Flesch Reading Ease (0–100): The most widely used readability test, developed by Rudolf Flesch in 1948. Higher scores mean easier reading. A score of 60–70 is ideal for general web content and blog posts. Scores below 30 are considered very difficult (academic papers, legal documents). The formula uses average sentence length and average syllables per word.
2. Flesch-Kincaid Grade Level: Converts the Flesch score into a US school grade level. A score of 8 means an 8th grader can understand the text. Aim for grade 6–8 for most web content; grade 10–12 for professional writing. Published in 1975 and still used by the US Department of Defense for military documents.
3. Gunning Fog Index: Developed by Robert Gunning in 1952 to measure the years of formal education needed to understand text on first reading. Uses sentence length and the percentage of "complex words" (3+ syllables). A score of 12 means a high school graduate can understand it; below 8 is easy for most readers.
4. Coleman-Liau Index: Unlike other formulas, uses characters per word rather than syllables, making it more consistent for automated analysis. Developed by Meri Coleman and T.L. Liau in 1975. Outputs a US grade level. Particularly useful for digital text where syllable counting may be inconsistent.
5. SMOG Index: Simple Measure of Gobbledygook, developed by G. Harry McLaughlin in 1969. Requires at least 30 sentences for accuracy. Estimates the years of education needed to understand a text. Often preferred for healthcare and government communications because of its proven accuracy.
6. Automated Readability Index (ARI): Developed in 1967 by the US Air Force to test the readability of technical manuals. Uses characters per word and words per sentence. Outputs a grade level from 1–14. Highly accurate for technical and professional writing.
Who needs a readability checker?
- Content marketers writing for broad audiences (aim for grade 6–8)
- Bloggers and journalists optimizing for SEO (Google prefers readable content)
- Academic writers checking if their work is accessible
- Healthcare professionals writing patient-facing communications
- Government and legal writers required to meet plain language standards
- ESL teachers assessing text difficulty for students
How to Use Our Readability Checker
Type or paste your text into the editor on the left. All six readability scores update instantly in the panels below. The Flesch Reading Ease score appears as the hero metric in the right sidebar with a circular gauge — this is the most widely recognized readability score.
Below the editor, the Score Cards show all six formulas with:
- The numerical score
- The equivalent US grade level
- A color indicator (green = easy, yellow = moderate, red = difficult)
- A brief interpretation
The sidebar also shows text statistics including average words per sentence, average syllables per word, and the count and percentage of complex words (polysyllabic words with 3+ syllables).
Tips for improving your readability score:
- Shorten sentences: Aim for 15–20 words per sentence on average
- Simplify vocabulary: Replace complex polysyllabic words with simpler alternatives
- Use active voice: Passive constructions often create longer, harder-to-read sentences
- Break up paragraphs: Short paragraphs improve visual readability even if the score stays the same
- Target your audience: A medical journal should score 40–50; a blog post should score 60–70
Frequently Asked Questions
What is a good readability score?
For general web content and blog posts, aim for a Flesch Reading Ease score of 60–70 (Grade 8–9 level). For professional and technical writing, 50–60 is acceptable. Academic and legal texts commonly score 30–50. The ideal score depends on your audience — always write at the reading level of your target reader.
What is the Flesch-Kincaid readability test?
The Flesch-Kincaid readability test is actually two formulas: the Flesch Reading Ease score (0–100, higher is easier) and the Flesch-Kincaid Grade Level (outputs a US school grade). Both use average sentence length and average syllables per word. The formulas were developed by Rudolf Flesch and J. Peter Kincaid and are among the most widely used readability measures in the world.
What is the Gunning Fog Index?
The Gunning Fog Index estimates the years of formal education needed to understand text on first reading. It was developed by businessman Robert Gunning in 1952 to improve the readability of newspapers and business writing. The formula uses average sentence length plus the percentage of complex words (words with 3 or more syllables). A score of 8 is readable by most adults; scores above 12 indicate difficult text.
What are complex words in readability formulas?
Complex words are words containing three or more syllables — also called polysyllabic words. Examples include 'understanding' (4 syllables), 'comfortable' (4 syllables), and 'approximately' (5 syllables). Both the Gunning Fog Index and SMOG Index use complex word counts. Reducing complex words is one of the most effective ways to improve your readability score.
How accurate is the SMOG Index?
The SMOG Index (Simple Measure of Gobbledygook) requires at least 30 sentences for accurate results. With fewer than 30 sentences, the score may be less reliable. SMOG is considered one of the most accurate readability formulas for predicting reading comprehension, particularly for healthcare and government communications. It was developed by G. Harry McLaughlin in 1969.
Does readability affect SEO?
Yes, readability indirectly affects SEO. Google's algorithms prioritize high-quality, user-friendly content. More readable content leads to lower bounce rates, longer dwell time, and better engagement signals — all positive ranking factors. Additionally, readable content is more likely to earn backlinks and social shares. For most websites, targeting a Flesch-Kincaid grade level of 7–9 is ideal for both user experience and SEO.
What is the Coleman-Liau Index?
The Coleman-Liau Index was developed by Meri Coleman and T.L. Liau in 1975. Unlike other readability formulas that count syllables, it uses characters per word, making it more consistent for computer-based analysis. The formula outputs a US grade level and is particularly useful for analyzing digital text, student essays, and academic papers.
What reading level should a blog post be?
Most successful blog posts and online articles target a reading level between Grade 6 and Grade 9 (Flesch-Kincaid Grade Level 6–9, or Flesch Reading Ease 60–80). This makes content accessible to the widest possible audience. Leading publications like the New York Times aim for Grade 10; BuzzFeed and popular blogs target Grade 6–8. Use a readability checker to verify your content hits your target level.