The TextKit Readability Checker scores your text on three of the most widely used readability formulas — Flesch Reading Ease, Flesch-Kincaid Grade Level, and the Gunning Fog Index — plus the underlying syllable and complex-word counts you need to compute SMOG yourself. Paste a paragraph or an entire article and get instant scores with grade levels and a plain-English interpretation.
Readability formulas aren't perfect — they measure surface features like sentence length and syllable count, not actual comprehension — but they're a fast, useful proxy. If your Flesch score is 30, your writing is probably too hard for a general audience. If it's 80, you're probably writing clearly. This tool is built for writers who want a quick gut check: content marketers, technical writers, educators, healthcare writers, and anyone producing text for a defined reading level.
How to use this tool
- Paste your text. Drop in a paragraph, a blog post, a patient handout, or anything else you want to score. Aim for at least 100 words for a stable score; a single short sentence gives noisy results.
- Read the scores. The checker shows Flesch Reading Ease (0–100, higher is easier), Flesch-Kincaid Grade Level (US grade number), Gunning Fog Index (grade number), plus syllable count and complex-word count (3+ syllables).
- Interpret the level. The Reading Level card translates the Flesch score into a grade band — from 'Very Easy (5th grade)' to 'Very Difficult (college)'.
- Adjust and re-check. To lower the grade level (make it easier), shorten sentences and replace multisyllabic words with shorter synonyms. To raise it, do the reverse.
How it works
The checker computes three scores, each based on the same three raw inputs: word count, sentence count, and syllable count. Words are tokens split on whitespace. Sentences are counted by matching terminal punctuation (. ! ?) followed by whitespace or end of text, with a minimum of 1 sentence for any non-empty input. Syllables use a heuristic: strip non-letters, return 1 for any word of three or fewer letters, then for longer words strip silent endings (-es, -ed, -e except after l or a) and count vowel groups (1–2 adjacent vowels = 1 syllable). This heuristic is fast and approximately correct — it agrees with dictionary syllable counts about 85% of the time, with most errors on unusual words.
The Flesch Reading Ease formula is: 206.835 - 1.015 × (words / sentences) - 84.6 × (syllables / words). It produces a score from 0 to 100 (and occasionally outside that range for extreme inputs) where higher means easier. The standard interpretation: 90+ is 5th-grade level (very easy), 60–70 is 8th–9th grade (standard), 30–50 is college level (difficult), and below 30 is graduate-level (very difficult).
The Flesch-Kincaid Grade Level formula is: 0.39 × (words / sentences) + 11.8 × (syllables / words) - 15.59. It converts the same inputs into a US grade number — a score of 8.0 means an 8th-grader could read it. This is the formula Microsoft Word uses in its built-in readability checker, and it's widely used in education and government.
The Gunning Fog Index formula is: 0.4 × ((words / sentences) + 100 × (complex_words / words)), where complex_words are words with three or more syllables. It produces a grade number directly. The “fog” metaphor refers to the obscurity added by long sentences and complex words. Fog tends to run a grade or two higher than Flesch-Kincaid on the same text because it penalizes complex words heavily.
The SMOG (Simple Measure of Gobbledygook) formula is: 1.0430 × √(complex_words × (30 / sentences)) + 3.1291, designed for texts of 30+ sentences (it samples polysyllabic word count). SMOG is widely used in healthcare for patient-education materials. Our tool surfaces the syllable and complex-word counts you need to compute SMOG yourself for shorter texts.
Worked example: take the sentence pair "The cat sat. The dog ran." That's 6 words, 2 sentences, and 6 syllables (every word is one syllable). Flesch = 206.835 - 1.015 × (6/2) - 84.6 × (6/6)= 206.835 - 3.045 - 84.6 = 119.2 — “very easy, kindergarten.” Flesch-Kincaid = 0.39 × 3 + 11.8 × 1 - 15.59 = -2.6 — effectively 0 (below 1st grade). Gunning Fog = 0.4 × (3 + 0)= 1.2. All three agree: this is extremely easy text.
Who uses this tool
Match your blog's reading level to your audience — most consumer content targets 8th-grade (Flesch 60–70).
Confirm that documentation isn't harder to read than it needs to be — long sentences and jargon compound quickly.
Match reading assignments to grade level — Flesch-Kincaid is widely used in K-12 and ESL materials.
Patient-education materials should target 6th-grade or below — SMOG and Flesch-Kincaid are the standard measures.
Plain Language laws require government communications to be readable — Flesch is the standard metric.
Microcopy and help text should score at least 60 on Flesch — users skim, they don't study.
Vary readability deliberately — dialogue scores higher (easier) than exposition; this creates rhythm.
Emails with Flesch 60+ get higher engagement — readers scan and bounce if sentences are too long.
Examples
Every word is one syllable; sentences are short. All three formulas agree this is extremely easy text.
Six words, all multisyllabic, one long sentence. Reads as graduate-level academic prose.
Marketing copy should aim for Flesch 60–80. This example is on the easy end of that range.
Tips & best practices
- Aim for Flesch 60–70 for general web content — that's 8th–9th grade, the level most adults read comfortably.
- Shorten sentences to lower the grade level — splitting one 25-word sentence into two 12-word sentences drops Flesch-Kincaid by about 1.5 grades.
- Replace multisyllabic words with shorter synonyms where possible — 'use' instead of 'utilize', 'help' instead of 'facilitate'.
- Score at least 100 words at a time — single-sentence scores are noisy and not representative.
- Healthcare and government content should target Flesch 70+ (6th grade or below) for accessibility compliance.
- Use the syllable and complex-word counts to diagnose why a score is high — if complex words are the problem, swap them; if sentence length is the problem, split sentences.
- Don't optimize readability at the expense of accuracy — some technical content genuinely needs to be at college level. Match the score to the audience, not to a universal target.
Common mistakes to avoid
- Treating readability scores as a measure of writing quality — a low score doesn't mean bad writing, it means hard reading. Sometimes you want hard reading.
- Scoring very short snippets — single sentences give unstable scores. Aim for at least 100 words.
- Trusting the syllable heuristic on unusual words — the heuristic agrees with dictionaries about 85% of the time and struggles with words like 'every' (counts as 2, should be 3) and 'business' (counts as 2, correct).
- Lowering the grade level by dumbing down content — replace jargon with plain language, not with vague words. 'Facilitate' → 'help' is good; 'facilitate' → 'thing' is bad.
- Forgetting that scores vary by section — dialogue scores easier than exposition. Score each section type separately for a useful picture.
“Readability scores are a smoke alarm, not a thermostat. They tell you something is wrong — usually a sentence that's too long or a word that's too fancy — but they don't tell you how to fix it. Use the score to find the problem, then use your judgment as a writer to fix it. The goal isn't a high Flesch score; the goal is writing your reader can actually follow.”
Frequently asked questions
▸What's a good Flesch Reading Ease score?
For general web content, aim for 60–70 (8th–9th grade). For consumer-facing content, 70+ is better. For technical or academic content, 30–50 may be appropriate. Below 30 is graduate-level and too hard for most general audiences.
▸How is the Flesch-Kincaid Grade Level calculated?
Using the formula 0.39 × (words/sentences) + 11.8 × (syllables/words) - 15.59. It's the same inputs as Flesch Reading Ease, scaled to a US grade number. A score of 8.0 means an 8th-grader could read it comfortably.
▸Why does Gunning Fog give a higher grade than Flesch-Kincaid on the same text?
Because Fog heavily penalizes complex words (3+ syllables). It counts them as a percentage of total words and adds that directly to the average sentence length. Flesch-Kincaid uses syllables-per-word instead, which spreads the penalty across all multisyllabic words, not just the 3+ syllable ones.
▸What is SMOG and why doesn't this tool compute it directly?
SMOG (Simple Measure of Gobbledygook) is a readability formula designed for healthcare: 1.0430 × √(complex_words × (30/sentences)) + 3.1291. It's calibrated for texts of 30+ sentences. Our tool surfaces the syllable and complex-word counts you need to compute SMOG yourself for shorter texts.
▸How accurate is the syllable counter?
The heuristic agrees with dictionary syllable counts about 85% of the time. It struggles with silent letters and unusual words ('every' counts as 2, should be 3; 'business' counts as 2, which is correct). For most prose, the small errors average out across a long text.
▸Does Google use readability as a ranking factor?
Not directly — Google has not confirmed using Flesch scores. But readability affects dwell time, bounce rate, and other engagement signals that do correlate with rankings. Writing clearly is good for users and indirectly good for SEO.
▸Can I score text in a language other than English?
The formulas are calibrated for English. Running them on other languages gives scores, but the grade-level interpretations don't transfer. For non-English text, use a readability formula designed for that language (e.g., the Fernandez Huerta formula for Spanish).
▸Why did my score come out negative or above 100?
Flesch Reading Ease can fall outside the 0–100 range for extreme inputs — very short, very simple text can score above 100, and very dense text can score below 0. This is normal. The interpretation bands (Very Easy, Very Difficult) still apply at the extremes.
Last reviewed and updated by Muhammad Umair. Have feedback or found an inaccuracy? Let us know.