Readability Checker: Flesch Reading Ease and Grade Level

What readability scores measure

Every classic readability formula measures the same two things: how long your sentences are and how long your words are. Long sentences make readers hold more in their head before they get to the point. Long words are, on average, less familiar. Neither formula knows whether your writing is clear, true, or well organized. They are a thermometer, not a diagnosis.

Used that way, they are very useful. A score tells you quickly whether a draft is in the right range for its audience, and it moves when you fix the two things that matter most. This checker computes six scores at once, in your browser, so you can paste a confidential draft without it being uploaded anywhere.

The six formulas

Flesch Reading Ease (1948): 206.835 − 1.015 × (words per sentence) − 84.6 × (syllables per word). It runs from about 0 to 100, and higher is easier. 60 to 70 is plain English; most newspapers land between 50 and 60; academic papers often score below 30.

Flesch-Kincaid Grade Level (1975): 0.39 × (words per sentence) + 11.8 × (syllables per word) − 15.59. It uses the same inputs, rescaled to a US school grade. A score of 8 means an average eighth grader can follow it. The US Navy developed it for training manuals, and many US government agencies still use it.

Gunning Fog Index: 0.4 × (words per sentence + 100 × complex-word ratio), where complex words have three or more syllables. It estimates years of formal education needed.

SMOG: 1.043 × √(polysyllables × 30 ÷ sentences) + 3.1291. It is popular in healthcare writing because it was validated against 100 percent comprehension, not 50 to 75 percent like the others. It is designed for samples of 30 or more sentences, and the checker warns you when your text is shorter.

Coleman-Liau Index: 0.0588 × L − 0.296 × S − 15.8, where L is letters per 100 words and S is sentences per 100 words. It counts letters instead of syllables, so it avoids syllable-counting errors entirely.

Automated Readability Index: 4.71 × (characters per word) + 0.5 × (words per sentence) − 21.43. Like Coleman-Liau, it uses characters, which is why it was popular for early typewriter-based counters.

What score should you aim for

For web pages, product copy, and emails, aim for a Flesch Reading Ease of 60 or higher and a grade level of 8 or lower. That is not dumbing down. Readers of all education levels prefer plain text, and they skim online. Health information for patients should target grade 6 to 8, a common recommendation from US health agencies. Legal and technical documents will score harder, and that is fine, as long as the difficulty comes from the subject rather than padding.

Worked example: fixing a hard sentence

Before: "Consequently, organizations that systematically overcomplicate their communication inevitably discover that comprehension deteriorates." That is 12 words and 44 syllables, and nine of the words have three or more syllables. Its Flesch-Kincaid grade comes out above 30, which is off the scale for any real reader.

After: "When companies make things hard to read, people stop reading." Ten words, 14 syllables, one complex word. The grade drops to about 5 and Reading Ease jumps to the high 70s. The meaning did not change; it got sharper. Two moves did it: keep the sentence short and swap long abstract words for short concrete ones.

Pitfalls

Syllable counts are estimates. Like most checkers, this one counts syllables with a rule-based heuristic (vowel groups, minus silent endings) rather than a pronunciation dictionary. It gets most common words right but can miss on names, abbreviations, and unusual words, so scores may differ by a few tenths from other tools. Coleman-Liau and ARI do not use syllables, so compare against them.

Sentence detection is punctuation-based. Abbreviations like e.g. or Dr. can be counted as sentence ends, which makes sentences look shorter and scores look easier. Bullet lists without periods look like one giant sentence and make scores look harder. Paste prose, not outlines.

Short text is noisy. Three sentences can swing a grade level by several points. Check at least 100 words, and 30 sentences for SMOG.

Do not write to the formula. Chopping every sentence into fragments raises your score and ruins your rhythm. Vary sentence length. Keep technical terms your readers actually use. Then use the longest-sentences list to find the two or three that need work.