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Readability Checker

Flesch Reading Ease

43.3

Difficult (college)

Sentences
5
Words
61
Avg words per sentence
12.2
Avg syllables per word
1.8

Grade-level scores

Flesch-Kincaid Grade
10.3
Gunning Fog
14.7
SMOG Index
13.0
Automated Readability Index
10.0
Coleman-Liau Index
13.4

Longest sentence (16 words)

The Flesch Reading Ease score measures how difficult a passage of English text is to understand.

Difficult words (3+ syllables)

consideredtypicallyacademicunderstanddifficultsyllablesmeasuresindicatecombinesreadable

Estimates for educational purposes — not financial, medical, or legal advice. See terms.

Score text readability with the six most common formulas in one place, plus see the longest sentence and the top 10 difficult words at a glance. Paste text into the box and the results update live.

The six formulas

Flesch Reading Ease — the original (1948). Formula:

206.835−1.015⋅wordssentences−84.6⋅syllableswords206.835 - 1.015 \cdot \frac{\text{words}}{\text{sentences}} - 84.6 \cdot \frac{\text{syllables}}{\text{words}}

Higher is easier. The score runs roughly from 0 (very hard) to 100 (very easy), though you can exceed that range with pathological input.

Flesch-Kincaid Grade Level — same inputs, different weights, expressed as a US school grade:

0.39⋅wordssentences+11.8⋅syllableswords−15.590.39 \cdot \frac{\text{words}}{\text{sentences}} + 11.8 \cdot \frac{\text{syllables}}{\text{words}} - 15.59

A score of 9.0 means “an average 9th-grade (age 14–15) student can read this”. Widely used because it’s easy to interpret.

Gunning Fog — weighs “complex” (3+ syllable) words heavily:

0.4⋅[wordssentences+100⋅complexwords]0.4 \cdot \left[ \frac{\text{words}}{\text{sentences}} + 100 \cdot \frac{\text{complex}}{\text{words}} \right]

Returns a grade level. Popular for business and technical writing where jargon density matters.

SMOG Index — designed for 30+ sentence texts, especially health writing:

1.0430⋅complex⋅30sentences+3.12911.0430 \cdot \sqrt{\text{complex} \cdot \frac{30}{\text{sentences}}} + 3.1291

Returns a grade level. Unreliable on short inputs.

Automated Readability Index (ARI) — uses characters instead of syllables, which makes it easier to compute mechanically:

4.71⋅characterswords+0.5⋅wordssentences−21.434.71 \cdot \frac{\text{characters}}{\text{words}} + 0.5 \cdot \frac{\text{words}}{\text{sentences}} - 21.43

Returns a grade level. Often gives slightly lower results than Flesch-Kincaid on the same input because character length is a cruder proxy for syllable count.

Coleman-Liau Index — another character-based formula:

0.0588⋅L−0.296⋅S−15.80.0588 \cdot L - 0.296 \cdot S - 15.8

where $L$ is the average letters per 100 words and $S$ is the average sentences per 100 words. Returns a grade level.

What “readability” actually measures

All six formulas essentially combine two intuitions:

  1. Longer sentences are harder — you have to hold more in working memory before the clause resolves.
  2. Longer words are harder — they’re typically rarer, more technical, and require more processing.

The formulas disagree on the exact weights, but they all push in the same direction: shorter sentences + shorter words = easier text. What they don’t measure:

  • Vocabulary difficulty beyond word length. “Ectoplasm” is 3 syllables; “chair” is 1. Both are equally common to a typical reader; neither is harder than the other in practice.
  • Grammatical complexity. A sentence with heavy nested clauses can be short in word count but hard to parse.
  • Conceptual difficulty. A simple sentence about quantum entanglement is still about quantum entanglement.
  • Coherence. A page with clear transitions and good structure is easier to read than the same words reshuffled, but no readability formula notices.

Treat the scores as a sanity check on sentence and word length, not as a final judgement on whether your writing is clear.

Example: simple text

“The cat sat on the mat. The dog ran fast. The sun was bright.”

  • Flesch Reading Ease: ~116 (off the standard scale, very easy)
  • Flesch-Kincaid Grade: ~−2 (below 1st grade)
  • Gunning Fog: ~1.7
  • All three algorithms agree this is trivially easy reading.

Example: complex text

“The multifarious complications of photosynthesis necessitate sophisticated biochemical understanding, particularly regarding chlorophyll-mediated electromagnetic energy transduction across thylakoid membranes.”

  • Flesch Reading Ease: ~−30 (extremely difficult)
  • Flesch-Kincaid Grade: ~25+ (post-graduate)
  • Gunning Fog: ~30+
  • All three push against the top of the scale.

Example: plain English target

Most general-audience writing (newspapers, popular science, product documentation) aims for:

  • Flesch Reading Ease: 60–70
  • Flesch-Kincaid Grade: 7–9
  • Gunning Fog: 8–10

If your draft scores higher (harder) than these targets, look at the longest-sentence output and consider breaking it up. If the difficult-words list contains jargon you can replace with simpler synonyms, replace them. If the jargon is non-negotiable (technical term of art, brand name), leave it — the hit to the score is the cost of doing business.

What this tool does not do

It doesn’t handle non-English text — the syllable counter and formulas are all tuned for English. Feeding Spanish or German text in will produce nonsense scores.

It doesn’t compute Dale-Chall readability, which requires a reference list of 3000 “easy” words. That’s a more accurate formula than the syllable-based ones but needs vocabulary data to work.

It doesn’t suggest rewrites or simplifications. You get the scores and the diagnostic data (longest sentence, difficult words); what to do about them is up to you. For spotting unconsciously repeated phrases in the same draft, the keyword density analyzer lists bigrams and trigrams; for simple word/character totals, the word counter is the fast answer.

Frequently asked questions

What is a good Flesch Reading Ease score?

It depends on your audience. 60–70 is 'plain English' — the range recommended for newspaper articles, consumer products, and general audience content. Above 70 is unusually easy (children's books, simple instructions). Below 50 starts feeling academic. Below 30 is college-textbook territory. Most technical writing lands between 40 and 60. The score is an imperfect proxy — you can write turgid text that scores 80 and readable text that scores 40 — but as a sanity check on average sentence length and average word length, it's useful.

Why are there six different formulas?

Because readability isn't a single well-defined thing, and each formula was designed for a different context. Flesch is from the 1940s for newspaper and magazine writing. Flesch-Kincaid is a US Navy adaptation that expresses the same idea as a grade level. Gunning Fog (1952) weighs 'complex words' (3+ syllables) heavily and is aimed at business writing. SMOG (1969) is designed specifically for 30+ sentence texts and health/medical content. Automated Readability Index uses character counts instead of syllables, which is easier to automate. Coleman-Liau is designed for newspaper-style content. They mostly agree within 1–2 grade levels; showing all six lets you see where they disagree and why.

Are the syllable counts exact?

No — English syllable counting is a heuristic, not a solvable problem with rules alone. This tool uses the classic vowel-group method: count groups of consecutive vowels, subtract trailing silent 'e', keep 'le' endings that add a syllable, minimum of 1 per word. It's accurate to within about 15% for random words and much closer to exact for aggregate counts over a paragraph or more. Anything relying on precise individual syllable counts (poetry scansion, metrics like mora timing) needs a real pronunciation dictionary, which this tool doesn't include.

Why does a single sentence give a weird score?

Because readability formulas were designed for paragraphs or longer texts, and their average-based statistics are unstable at small sample sizes. A single sentence of 15 words with one 4-syllable word produces different results from a 1000-word document where the same ratio holds steady. SMOG in particular expects at least 30 sentences to stabilize — on short inputs it becomes unreliable. Take any result from a 1–2 sentence input with a large grain of salt.

What counts as a 'difficult word'?

A word with three or more syllables, which is how Gunning Fog and SMOG define 'complex words'. The definition is crude — 'language' is 3 syllables and feels easy, while 'sleigh' is 1 syllable and feels arcane — but it correlates with reading difficulty well enough in aggregate. The tool lists the top 10 such words by syllable count so you can see which vocabulary is pushing up the scores. Sometimes you can swap them out for simpler synonyms; sometimes the word is the right one and the readability hit is worth it.