Flesch-Kincaid Readability Score — Reading Ease + Grade Level

Two scores, and they move in opposite directions

This panel shows two numbers, and confusing them is the most common mistake made with either. Flesch Reading Ease runs 0-100 and higher is easier. Flesch-Kincaid Grade Level is a US school year and higher is harder. Reading "72" as a grade level, or "12" as a reading-ease score, inverts the meaning of your own text.

Reading Ease = 206.835 - 1.015 x (words per sentence) - 84.6 x (syllables per word)

Grade Level = 0.39 x (words per sentence) + 11.8 x (syllables per word) - 15.59

Both formulas have exactly two inputs

Average words per sentence, and average syllables per word. That is everything. Neither formula can see vocabulary choice, logical order, whether an example lands, whether a paragraph follows from the one before it, or whether the text is true.

The consequence is the useful part: you can always improve the score without improving the writing. Halve every sentence, swap every long word for a short one, and both numbers move the way you wanted while the prose gets choppier and starts to read as though it distrusts the reader. Nothing in the formula can object.

So treat the score as a smoke detector, not a judge. A bad score is a reliable prompt to go and look — something really is long or dense. A good score is not evidence of anything, because the two things it measures are the two things easiest to fake.

How the two scores come apart

They usually track each other, but not always, and the exception is worth knowing. Syllables carry roughly 83 times the weight of sentence length in the reading-ease formula, and only about 30 times in the grade-level one. So long sentences built from short words pull them apart.

A real case: one 41-word sentence made entirely of one-syllable words scores 80.6 reading ease — the "easy" band — and a grade level of 12.2, the final year of school. Every word is simple and the sentence is still exhausting. When the two disagree like that, the grade level is usually telling you the truth, and the fix is a full stop rather than a shorter word.

The bands, and who they are for

• 90+ 5th grade, very easy
• 80-89 6th grade, easy
• 70-79 7th grade, fairly easy
• 60-69 8th-9th grade, plain
• 50-59 10th-12th grade, fairly hard
• 30-49 college, hard
• Under 30 college graduate, very hard

Plain to fairly easy suits general audiences, and it is worth being blunt about why: it is not that readers cannot manage harder prose, it is that on the web they are deciding whether to bother. Specialist writing for specialist readers legitimately scores harder, and forcing an academic paper into the easy band would strip out the precision its readers came for. The target follows the audience, not the other way round.

Where the numbers are approximate

Syllables are counted by heuristic — vowel groups, minus a trailing silent e. It is right on most ordinary words and wrong in both directions on some common ones: it reads business and every as three syllables and beautiful as four, while giving create one and idea two. Errors that frequent cancel out across a few hundred words, which is why the score is usable on an article and unreliable on a sentence.

Both formulas are calibrated on English. If the text you paste is mostly not in Latin script, a warning appears above the results saying the score is not meaningful for it; the numbers are still displayed, because the word and sentence counts remain perfectly valid and only the readability score should be ignored.

For the other half of the picture — how long the finished piece takes to get through — see the reading time estimator.