π Readability Checker
Analyze text readability using 5 established formulas.
π 100% client-side processing
This Readability Checker scores your text with five established formulas β Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog, SMOG, and the Automated Readability Index β plus a consensus grade that averages them. Paste a draft and watch the numbers update as you type. It is built for writers, editors, teachers, and SEO specialists who need their words to land with real readers.
The Five Scores and What They Measure
| Score | Scale | Inputs it weights |
|---|---|---|
| Flesch Reading Ease | 0β100, higher is easier | Sentence length and syllables per word |
| Flesch-Kincaid Grade | US school grade | The same two inputs, mapped to grades |
| Gunning Fog | US school grade | Sentence length and share of 3+ syllable words |
| SMOG | US school grade | Count of polysyllabic words |
| Automated Readability Index | US school grade | Characters per word and sentence length |
The panel also shows the raw statistics behind them: word count, sentence count, syllable count, complex-word count, and average words per sentence. Those five numbers explain almost every disagreement between the scores.
How the Formulas Work
Nearly every formula balances two pressures: long sentences force readers to hold more in working memory, and long words tend to be less familiar. Flesch Reading Ease combines them as 206.835 β 1.015 Γ (words Γ· sentences) β 84.6 Γ (syllables Γ· words). A higher score means easier reading, and 60β70 is comfortable for most adults. Flesch-Kincaid uses the same two ratios but outputs a grade: 0.39 Γ (words Γ· sentences) + 11.8 Γ (syllables Γ· words) β 15.59.
Gunning Fog counts words of three or more syllables as βcomplexβ: 0.4 Γ (avg sentence length + 100 Γ complex-word ratio). SMOG weighs only polysyllables, 1.043 Γ β(polysyllables Γ 30 Γ· sentences) + 3.1291, which is why it needs at least three sentences to behave. ARI swaps syllables for characters, 4.71 Γ (characters Γ· words) + 0.5 Γ (words Γ· sentences) β 21.43, making it the easiest to compute without pronunciation guesses.
All five share the same approximate syllable counts, generated by a heuristic English syllable counter, so they are not fully independent. If that counter misreads a cluster of technical terms, several scores move together in the same direction. The consensus grade deliberately excludes Flesch Reading Ease, because averaging a 0β100 ease score with grade levels would mix incompatible scales; it averages the grade-level formulas instead and includes SMOG only when SMOG is valid.
Worked Example: Scoring a Short Passage
Suppose a sample paragraph measures 20 words in 2 sentences, with 30 syllables, 2 complex words, and an average word length of 5 characters. Feed those numbers into each formula:
- Flesch Reading Ease:
206.835 β 1.015Γ10 β 84.6Γ1.5 = 69.8(Standard) - Flesch-Kincaid Grade:
0.39Γ10 + 11.8Γ1.5 β 15.59 = 6.0 - Gunning Fog:
0.4 Γ (10 + 100Γ0.10) = 8.0 - ARI:
4.71Γ5 + 0.5Γ10 β 21.43 = 7.1 - SMOG: 0, because two sentences is below the three-sentence minimum
- Consensus Grade:
(6.0 + 8.0 + 7.1) Γ· 3 = 7.0
The reading-ease score says the passage is comfortable, while the grade scores cluster around middle school. The spread is normal and is why the tool leads with a range of evidence rather than a single verdict.
What Counts as Good
Flesch Reading Ease maps to seven labelled levels, from Very Easy (90+) through Standard (60β69) to Very Difficult (below 30). The badge also shows a recommended audience, from 5th grade up to college graduate. For public-facing web copy, Standard or easier is a safe target; government and healthcare plain-language guidance often pushes toward grade 6β8, which usually means shorter sentences and plainer vocabulary.
| Reading Ease | Label | Typical audience |
|---|---|---|
| 90β100 | Very Easy | 5th grade |
| 80β89 | Easy | 6th grade |
| 70β79 | Fairly Easy | 7th grade |
| 60β69 | Standard | 8thβ9th grade |
| 50β59 | Fairly Difficult | 10thβ12th grade |
| 30β49 | Difficult | College |
| 0β29 | Very Difficult | College graduate |
The mapping is not a scoreboard of quality. A childrenβs story and a legal disclaimer are both βcorrectβ for their audiences, and a technical audience may prefer precise vocabulary over a low grade level. Read the label as βwho can comfortably follow this,β not βhow good is this.β
Common Mistakes and Edge Cases
- Judging on too little text. Under 50 words the tool shows a warning, and under three sentences SMOG is suppressed. Aim for at least 100β200 words before drawing conclusions.
- Writing to the number. Inflating scores by deleting every long sentence can strip nuance. The score is a diagnostic, not the goal.
- Ignoring the raw counts. If the consensus grade is high, check whether the cause is one sprawling sentence or a cluster of jargon; the fix differs.
- Treating lists as prose. Unpunctuated bullet lists collapse into one enormous sentence and distort every formula.
- Optimising for the wrong metric. Raising Flesch Reading Ease by shortening every sentence can produce a choppy, robotic rhythm. The score cannot see rhythm, so a human pass is still required.
Limitations of Automated Readability
These formulas count surface features β syllables, characters, sentence length β and cannot judge whether a sentence actually makes sense, whether a transition is missing, or whether a term is defined. They are English-calibrated, and the syllable counter is a heuristic that mis-handles some proper nouns and technical terms. Use the dashboard to find sentences worth rewriting, then decide with your own reading of the text.
Related Tools
Frequently Asked Questions
Why does the SMOG score show 0?
SMOG is designed for passages of at least three sentences and is unstable on very short samples. The tool returns 0 when your text has fewer than three sentences, while still showing the other four scores. Add a sentence or two and refresh to get a meaningful SMOG number.
Why do the five scores disagree with each other?
They measure different things. Flesch Reading Ease weighs sentence length against syllables per word and outputs a 0β100 scale. Flesch-Kincaid, Gunning Fog, and ARI all output school grades but weight sentence length, syllables, complex words, and characters differently. SMOG looks only at polysyllabic words. Divergence is expected; the Consensus Grade averages the grade-level scores (including SMOG only when it is valid) to give one number to track.
Does the checker work for languages other than English?
It counts words in any Unicode script, so it will produce numbers for Spanish, German, or French. But the syllable counter is built around English sound patterns, and several formulas were calibrated on English text, so non-English scores should be treated as rough directional signals rather than valid readability levels.
What counts as a complex word?
Any word the checker's syllable counter finds with three or more syllables. That is the classic Gunning Fog definition. It can be fooled: a familiar three-syllable word still counts, and proper nouns or hyphenated compounds can inflate the total without making the text harder.
Should I optimize for Flesch Reading Ease or for grade level?
For general web content, aim for a Flesch Reading Ease of roughly 60β70, which the checker labels Standard, and treat the grade-level scores as a secondary check. For a specific audience, pick the grade instead β many plain-language standards require grade 6β8. Changing sentence length and word choice moves both in the same direction.
Do headings, lists, and punctuation affect the score?
Punctuation decides where sentences end: the checker splits on periods, question marks, and exclamation points, so a long bulleted list without terminal punctuation can be counted as one very long sentence. Words are runs of letters and numbers, so markdown symbols are ignored but numbers themselves count as words.
Reviewed by the HandyTools Hub team Β· Last updated