Readability Calculator

About the Readability Calculator

The readability calculator analyses any text and instantly computes five established readability scores — Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog Index, SMOG Index, and Automated Readability Index — giving you a comprehensive, multi-metric view of how difficult your writing is for your target audience to understand. Readability matters far more than most writers realise. Research consistently shows that readers abandon content that is too complex for their comprehension level — and this is true even for highly educated readers. Academic research, legal documents, and government communications are notoriously written at reading levels far above their intended audience, reducing comprehension and compliance. The UK government's plain English campaign estimates that unclear government writing costs British businesses and citizens billions of pounds annually through misunderstanding and error. The US readability standard for public communications is a Grade 8 reading level — readable by the average adult. The NHS, the US Centers for Disease Control (CDC), and major news organisations like the BBC and Associated Press all target a Flesch Reading Ease score above 60 for public-facing content. The Flesch Reading Ease score (0–100) is the most widely used readability measure. Higher scores indicate easier reading: 90+ is very easy (children's books), 60–70 is the standard target for most consumer content, 30–50 is college-level difficulty, below 30 is professional or academic. The score is calculated from average sentence length and average syllables per word — two variables that individually explain most of the variance in reading difficulty. The Flesch-Kincaid Grade Level converts the same two variables into a US school grade level approximation, making it easy to understand your content's level relative to educational benchmarks. The Gunning Fog Index emphasises complex words (three or more syllables) in addition to sentence length, making it particularly sensitive to jargon and technical vocabulary. The SMOG Index (Simple Measure of Gobbledygook) was specifically designed for healthcare content and is widely used to assess medical materials for patient comprehension — it is considered the most accurate predictor of comprehension in health literacy contexts. The Automated Readability Index uses character count rather than syllable count, making it more consistent across different automated systems. Using all five metrics together gives a more robust picture than any single score alone — text that scores well on all five is genuinely accessible, while text that scores poorly on multiple metrics almost certainly needs revision.

How It Works

Flesch Reading Ease = 206.835 − (1.015 × avg words/sentence) − (84.6 × avg syllables/word). Flesch-Kincaid Grade = 0.39 × (words/sentences) + 11.8 × (syllables/words) − 15.59. Gunning Fog = 0.4 × (avg words/sentence + 100 × complex word%). SMOG = 3 + sqrt(complex words × 30/sentences). ARI = 4.71 × (chars/words) + 0.5 × (words/sentences) − 21.43. Complex words = words with 3+ syllables. Reading time assumes 238 words per minute (average adult reading speed). Example: 'The quick brown fox jumps over the lazy dog.' Words: 9. Sentences: 1. Syllables: 11. Avg words/sentence: 9. Avg syllables/word: 1.22. Flesch RE = 206.835 − 9.135 − 103.3 = 94.4 (Very Easy). FK Grade = 3.51 + 14.6 − 15.59 = 2.5 (Grade 2-3).

Tips & Best Practices

• ✓Target Flesch Reading Ease above 60 for most consumer-facing content. News articles (BBC, Guardian) typically score 60-70. Blog posts should aim for 65-75. Legal documents typically score 20-30, which is why they are so hard to read — this is not a regulatory requirement, just poor writing convention.
• ✓The single most impactful change you can make to improve readability is shortening your sentences. Average sentence length above 25 words almost always produces poor Flesch scores. Aim for an average of 15-18 words, with variation between very short (5-8 words) and moderately long sentences.
• ✓Replace latinate and technical vocabulary with common Anglo-Saxon alternatives wherever possible: 'utilise' → 'use', 'approximately' → 'about', 'commence' → 'start', 'terminate' → 'end', 'facilitate' → 'help'. Every reduction in syllables per word raises your Flesch score.
• ✓Active voice is shorter and clearer than passive voice. 'The report was written by the team' (8 words) → 'The team wrote the report' (5 words). Shorter active sentences improve every readability metric simultaneously.
• ✓The SMOG Index is specifically validated for health literacy contexts. If you are writing patient information, discharge instructions, or public health materials, SMOG is your most important score — target SMOG below 8 for general patient audiences and below 6 for low-literacy populations.
• ✓Readability scores are calibrated for prose. Technical content with unavoidable jargon, code samples, or specialist terminology will naturally score lower — this is acceptable if your audience is expert. The scores are most useful when writing for mixed or non-specialist audiences.
• ✓Reading time at 238 words per minute is the average for adult silent reading. Your actual audience may read faster (skim-reading on web pages) or slower (careful reading of legal or technical documents). Web content engagement data typically shows users reading 20-28% of words on a page.
• ✓Gunning Fog above 12 is considered too difficult for a general audience. Many business emails and reports score 14-18. Reducing to below 12 by shortening sentences and reducing jargon almost always improves communication effectiveness.

Who Uses This Calculator

Content writers and SEO professionals checking blog posts, articles, and landing pages for readability before publishing — Google's ranking algorithms favour clear, accessible content. Healthcare writers producing patient education materials, informed consent documents, and health communications where comprehension directly affects patient outcomes. Technical writers reviewing user manuals, help documentation, and software guides for clarity. Government and legal writers assessing communications for plain English compliance. Teachers grading the readability of student writing samples. Publishers evaluating manuscripts against their target audience reading level. Email marketers checking newsletter copy for readability before sending to mass audiences.