Readability Calculator | Grade Level & Scores

The Readability Calculator measures how easy your text is to read and understand, using four industry-standard readability formulas: Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog Index, and SMOG Grade. Paste any text and see your readability scores instantly, along with sentence-by-sentence analysis and a complex word breakdown — all the information you need to identify and simplify difficult passages before publishing.

Readability directly affects how effectively your audience receives your message. The Plain Language guidelines used by US government agencies and the NHS recommend a grade level of 8 or below for general public communications. Web content with better readability has lower bounce rates, higher time on page, and stronger engagement metrics. Academic writing, legal documents, and technical documentation intentionally target higher grade levels — but even in those fields, unnecessarily complex sentences reduce comprehension speed and increase cognitive load. Use this free readability checker to calibrate your writing for its intended audience.

Understanding the Four Readability Formulas

This readability score calculator runs four separate formulas simultaneously, each measuring different aspects of text complexity. Understanding what each formula measures helps you choose which score to optimise for your audience and purpose.

The Flesch Reading Ease score (0–100) is the oldest and most widely used readability formula, developed by Rudolf Flesch in 1948 for US Navy training manuals. Higher scores mean easier text. A score of 90–100 is understood by an average 11-year-old; 60–70 matches standard newspaper prose; 0–30 is university-level academic text. The score penalises long sentences and polysyllabic words. Most web content should target 60–80.

The Flesch-Kincaid Grade Level translates the same reading ease measurement into a US school grade level. Grade 6 is a typical sixth-grader; Grade 12 is a high school senior; Grade 16 is a college graduate. This formula is used by the US Department of Defense for technical manuals, by the FDA for drug labelling, and by many journalistic style guides. The Guardian targets Grade 8; the BBC targets Grade 9. Most content for a general adult audience should aim for Grade 8–10.

The Gunning Fog Index, developed by Robert Gunning in 1952, is calculated from average sentence length and the percentage of complex words (three or more syllables). It tends to produce slightly higher grade estimates than Flesch-Kincaid for the same text, because it weights complex vocabulary more heavily. Fog scores above 17 are considered virtually unreadable by most audiences.

The SMOG Grade (Simple Measure of Gobbledygook) was developed by G. Harry McLaughlin in 1969 specifically for health literacy assessments. Studies show SMOG correlates highly with actual reading comprehension for patient education materials, making it the preferred metric for healthcare, public health, and consumer safety contexts. The US National Cancer Institute and CDC recommend targeting SMOG Grade 6 or below for health information intended for the general public.

What Counts as a Complex Word?

All four formulas use "complex words" as a key input, and all define them the same way: words with three or more syllables. The syllable counter estimates syllable count using vowel group analysis — counting clusters of vowels (a, e, i, o, u, y) after removing a trailing silent 'e'. This is an approximation; English syllabification has many exceptions. Common false positives include proper nouns with many syllables, technical terms that are familiar to the audience, and compound words that read easily despite their syllable count. Treat the complex word list as a starting point for review, not a definitive list of words to eliminate.

Why Readability Matters for SEO and Engagement

Search engines measure user engagement signals including time on page, scroll depth, and bounce rate. Readable content keeps visitors on the page longer, increasing these positive signals. Google's own documentation on helpful content explicitly mentions that content should be written for the intended audience at an appropriate level — neither dumbed down nor unnecessarily complex. Beyond SEO, email open and click-through rates, social media shares, and conversion rates all correlate with readability. Studies by Nielsen Norman Group found that users read about 20% of the words on a web page; short sentences and simple vocabulary help more of that 20% carry your key message.

Readability for Different Content Types

Different content types have different appropriate grade levels. Email newsletters targeting professionals: Grade 9–11. Product landing pages for consumers: Grade 7–9. News articles: Grade 8–10. Academic journal papers: Grade 14–18. Legal contracts: Grade 12–16 (though plain language reforms are reducing this). Medical consent forms: Grade 8 or below (recommended by health literacy research). Children's educational content: Grade 2–5. Technical documentation for experts: Grade 12–14. Knowing the right target for your content type is as important as knowing your current score.