Readability Checker

How to Use the Readability Checker

1. Paste your text into the input area - an article, blog post, email, lesson plan, or any piece of English prose of 100 words or more.
2. Review the four scores - Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog Index and Coleman-Liau Index are calculated instantly in your browser.
3. Check the grade label next to each score for a plain-English interpretation (for example "Plain English", "Fairly Difficult", "College Graduate").
4. Edit and re-run - shorten long sentences, split complex paragraphs and swap multi-syllable words for shorter alternatives, then paste the new version to see the reading level drop.

About Readability Formulas

Readability formulas estimate how difficult a passage is to read based on measurable surface features - typically average sentence length (ASL) and average syllables per word (ASW) or the share of complex words. They cannot judge logic, relevance or accuracy, but they give a consistent signal that correlates well with comprehension tests.

The Flesch Reading Ease formula (Rudolf Flesch, 1948) is 206.835 - 1.015 x ASL - 84.6 x ASW. Scores from 90-100 read at a 5th-grade level, 60-70 are "Plain English" aimed at a typical 8th-9th grader, and below 30 requires a university degree. The Flesch-Kincaid Grade Level (US Navy, 1975) rewrites the formula as 0.39 x ASL + 11.8 x ASW - 15.59, producing a US school-grade number directly. People often refer to this as the "FK score" or "Flesch-Kincaid test".

The Gunning Fog Index (Robert Gunning, 1952) uses 0.4 x (ASL + 100 x complex/total), where complex words have three or more syllables. The Coleman-Liau Index (1975) skips syllables entirely and relies on 0.0588 x L - 0.296 x S - 15.8, where L is letters per 100 words and S is sentences per 100 words - easier to compute mechanically.

Two related formulas you may have seen elsewhere are SMOG (Simple Measure of Gobbledygook, McLaughlin 1969) and the Fry Readability Graph (Edward Fry, 1968). SMOG samples polysyllabic words from three 10-sentence chunks; Fry plots average sentence length against syllables on a chart that maps to a grade level. Both correlate strongly with the four scores reported here, so a passage that reads as Grade 9 on Flesch-Kincaid will land in the same band on SMOG or Fry. We report the four formulas above because they cover the same range using different inputs (syllables vs letters, raw counts vs complex-word ratio), so disagreement between them is a useful signal that one part of your text is unusual.

Automated Readability Index (ARI) and SMOG: When and Why

Two extra formulas that often appear in academic and clinical contexts are the Automated Readability Index (Smith and Senter, 1967) and SMOG (McLaughlin, 1969). ARI uses 4.71 x (characters / words) + 0.5 x (words / sentences) - 21.43 and outputs a US grade level - like Coleman-Liau it sidesteps syllable counting, which makes it robust on technical vocabulary. SMOG samples polysyllabic words from three 10-sentence chunks and converts the count via 1.0430 x sqrt(polysyllables x 30 / sentences) + 3.1291. Healthcare communicators favor SMOG for patient leaflets because the formula was validated against 100 percent comprehension targets, while general-purpose writers stick with Flesch-Kincaid because it correlates more directly with school-grade rubrics. Across the same 100-word passage, ARI typically lands within one grade of Flesch-Kincaid, and SMOG usually within two grades. The four scores reported above already cover the same range as ARI and SMOG, so adding more formulas adds little new information for general English prose.

Worked Examples: Three Texts at Three Grade Levels

• Hemingway, "The Old Man and the Sea" (excerpt): short sentences, mostly one or two-syllable Anglo-Saxon vocabulary. Flesch Reading Ease ~85, Flesch-Kincaid Grade ~4. Reads at a US 4th-grade level - intentional, because Hemingway's craft was compression.
• Wikipedia, "Solar System" lede: medium sentences (~20 words), moderate Latinate vocabulary ("planetesimal", "asteroid"). Flesch Reading Ease ~50, Flesch-Kincaid Grade ~10. Reads at a US 10th-grade level - representative of general-knowledge encyclopedic prose.
• SaaS terms-of-service paragraph: long compound sentences (~35 words), heavy modal stacking ("notwithstanding the foregoing"), legal Latin ("indemnify"). Flesch Reading Ease ~25, Flesch-Kincaid Grade ~17. Reads at graduate level - inaccessible to the average consumer, which is exactly why the EU and several US states now mandate plain-language summaries.

Run the same three sources through this readability score checker and watch how each formula reacts: ARI and Coleman-Liau move with sentence/letter counts; Flesch and Gunning Fog react more to vocabulary. If you also want a clean word and sentence count alongside the readability score, paste the same text into the word counter; for raw character counts (useful for character-limit comparisons), use the character counter.

Why We Report Four Scores Together

Single-formula readability tools can be misled by edge cases. A page full of short, common but multi-clause sentences fools syllable-based formulas; a page of long technical words inside short sentences fools sentence-length-based ones. Cross-checking against four independent formulas catches these patterns:

• Flesch Reading Ease and Flesch-Kincaid Grade share inputs but invert the scale - they should always agree on direction. A mismatch usually means a typo in the syllable count.
• Gunning Fog reacts to complex words specifically. If Fog jumps but Flesch holds steady, you have introduced jargon without lengthening sentences.
• Coleman-Liau uses character counts only, so it is immune to syllable miscounts on uncommon words. If Coleman-Liau disagrees with the others, your text likely contains specialist vocabulary that the syllable heuristic is mis-counting.

Score Interpretation

• Flesch Reading Ease 60-70 - Plain English, 8th-9th grade - ideal for general audiences, news sites and most marketing copy.
• Reading Ease 50-60 - Fairly difficult, 10th-12th grade - suitable for Wikipedia articles or trade publications.
• Reading Ease 30-50 - College level - academic writing, finance, medicine, legal.
• Reading Ease below 30 - Very difficult, graduate level - research papers and dense technical manuals.

Use Cases for the Reading Level Checker

• Writers and editors - run drafts through the reading level checker before publishing. Catch sentences that crept above 30 words and dense paragraphs that bury the lead.
• Teachers and curriculum designers - confirm that a worksheet or reading passage actually matches the target grade level. The writing grade level analyzer also helps when adapting age-appropriate versions of the same source.
• SEO content teams - Google's Helpful Content updates reward pages that match user intent. A consumer how-to scoring at Grade 12 is signalling expert audience to a beginner reader.
• ESL learners and tutors - reading level analyzers help select practice texts that stretch a learner without overwhelming them. Aim for one grade above the student's tested level.
• Academic and clinical writers - many journals and consent-form regulators specify a maximum Flesch-Kincaid grade. Run the readability checker before submission to catch over-complex passages.
• Plain-language compliance - government forms in the US, UK, Australia and EU often require Grade 8 or below. Use the readability score to verify before the legal review.

Tips to Improve Readability

• Target 15-20 words per sentence on average; split anything over 25.
• Prefer short, common words ("use" over "utilize", "help" over "facilitate").
• Break long paragraphs - 3-5 sentences each is a good web rhythm.
• Use active voice and concrete subjects; passive constructions inflate word count without adding clarity.
• Replace jargon with a plain-language equivalent on first mention, then define the term in parentheses.