About this tool
Readability formulas estimate how easy or difficult a piece of text is to understand. They are calculated from measurable properties of the text — primarily sentence length and word complexity (measured in syllables or characters). Readability scores do not evaluate content quality, meaning, or accuracy; they measure only surface-level linguistic complexity as a proxy for reading difficulty.
Flesch Reading Ease is the most widely used readability metric. It is calculated as: 206.835 − (1.015 × average sentence length) − (84.6 × average syllables per word). Scores range from 0 to 100. A score of 90–100 is considered very easy (readable by an average 11-year-old); 60–70 is plain English suitable for most adults; 30–50 is difficult (university level); below 30 is very difficult (professional or academic). Microsoft Word's readability statistics and many SEO tools use this formula.
Flesch-Kincaid Grade Level converts the same underlying variables into a US school grade approximation: (0.39 × average sentence length) + (11.8 × average syllables per word) − 15.59. A score of 8 means the text is readable by a typical 8th-grade student. A score of 12 corresponds to high school senior level. Most general-audience web content targets a grade 6–8 level. Technical documentation and academic writing typically scores 12–16.
Gunning Fog Index estimates the years of formal education a reader needs to understand a text on first reading. It is calculated as: 0.4 × (average sentence length + percentage of words with 3+ syllables). A score of 12 suggests high school level; below 8 is accessible to most adults. The index was developed by Robert Gunning in 1952 and is widely used in business writing and journalism. The Wall Street Journal and Time magazine typically score around 11–12.
SMOG (Simple Measure of Gobbledygook) was designed specifically for healthcare literacy assessments and is widely used in medical and public health writing. It estimates grade level based on polysyllabic word density. It requires at least 30 sentences for accuracy. A SMOG score of 10 means the text can be understood by someone with a 10th-grade education. US health literacy guidelines typically recommend patient-facing materials target a SMOG score of 6 or below.
Practical Usage Examples
Blog post check
Test a blog post introduction to ensure it targets a general adult audience.
Paste your intro paragraph. Aim for Flesch Reading Ease 60–70 and FK Grade Level 6–8 for broad accessibility.Medical content audit
Check patient-facing health content against recommended literacy levels.
Health guidelines recommend SMOG ≤ 6 and Flesch Reading Ease ≥ 70 for patient-facing materials.Step-by-Step Instructions
Paste your text (at least 50 words is recommended for accurate scores) into the input field.
Click "Calculate" — the tool instantly analyses syllables, words, and sentences in your browser.
Review the Flesch Reading Ease score (0–100, higher is easier), Flesch-Kincaid Grade Level (US school grade), SMOG Index, and Gunning Fog Index.
Use the advice panel to identify sentences that are too long or vocabulary that raises complexity.
Revise your text and recalculate to track readability improvements.
Core Benefits
Instant results with no waiting or processing delays
100% free to use with no sign-up, registration, or premium tiers
Complete privacy - all processing happens in your browser
Works offline once the page is loaded
Mobile-friendly responsive design for any device
Clean, focused interface without distractions
Bookmark-friendly for quick access anytime
Frequently Asked Questions
It depends on the audience. For general web content aimed at adults, target a Flesch Reading Ease of 60–70 and a Flesch-Kincaid Grade Level of 6–8. For children or broad public audiences, aim higher (Flesch 70–90). For academic or technical writing, a lower Flesch score is expected and acceptable. Healthcare organisations recommend SMOG ≤ 6 for patient-facing materials.
Flesch Reading Ease is a score from 0 to 100 that estimates how easy a text is to read. It is calculated as: 206.835 − (1.015 × average sentence length) − (84.6 × average syllables per word). Higher scores mean easier reading. Scores of 90–100 are very easy; 60–70 is standard adult reading; below 30 is very difficult academic or technical text.
The Flesch-Kincaid Grade Level formula converts readability into a US school grade number. A score of 8 means the text can be understood by a typical 8th-grade student. It is calculated as: (0.39 × average sentence length) + (11.8 × average syllables per word) − 15.59. Most consumer-facing web content targets grade 6–8.
The Gunning Fog Index estimates the years of formal education needed to understand a text. It is calculated as: 0.4 × (average sentence length + percentage of words with 3 or more syllables). A score of 12 corresponds to high school senior level. Most business and journalism targets a score below 12. It was developed by Robert Gunning in 1952.
SMOG (Simple Measure of Gobbledygook) is a readability formula that estimates grade level based on the count of polysyllabic words (3+ syllables). It is widely used for healthcare and medical writing. A SMOG score of 6 means 6th-grade reading level. US health communication guidelines recommend patient materials target a SMOG score of 6 or below. It requires at least 30 sentences for statistical accuracy.
The two most effective improvements are: (1) Shorten sentences — aim for an average of 15–20 words per sentence. Break long compound sentences into two. (2) Use simpler words — replace polysyllabic vocabulary with shorter synonyms where possible (e.g. "use" instead of "utilise", "help" instead of "facilitate"). Both reduce the Flesch-Kincaid and Gunning Fog scores.
Most readability formulas are designed for full documents or long paragraphs. A minimum of 100 words is recommended for reliable results; 200+ words gives better statistical accuracy. SMOG requires at least 30 sentences. Scores from very short texts (under 50 words) can be misleading due to the small sample size.
Google does not use readability scores as a direct ranking factor. However, readability strongly affects user behaviour metrics — time on page, bounce rate, and scroll depth — which are indirect signals of content quality. Easier-to-read content also earns more backlinks and social shares. Yoast SEO and similar tools include readability checks because readable content generally performs better in search.
Flesch Reading Ease (0–100 scale) and Flesch-Kincaid Grade Level (school grade scale) both use the same underlying variables (sentence length and syllables per word) but present the result differently. Reading Ease is inversely related to Grade Level — a high Reading Ease score (easy text) corresponds to a low Grade Level number, and vice versa.
Yes. All analysis is performed entirely in your browser using JavaScript. Your text is never sent to any server, stored in a database, or processed anywhere outside your own device. You can safely paste confidential drafts for readability analysis.
For general-audience blog content, target a Flesch Reading Ease of 60–70 and a Flesch-Kincaid Grade Level of 6–8. This is equivalent to the reading level of popular newspapers and magazines. Content targeting professionals in a specific field can reasonably target grade 10–12 without alienating readers.
Yes. This readability score calculator is completely free with no registration, no usage limits, and no premium tier.