Flesch Kincaid Readability Test

What This Measures

Both formulas work from two inputs: average sentence length and average syllables per word. Reading Ease returns a number from roughly 0 to 100 where higher is easier. Grade Level converts the same inputs into a US school grade, so a result of 8 means an average eighth grader could follow it.

Because the inputs are only length and syllable count, the formulas are blind to meaning. A page of grammatically simple nonsense scores well. A precise technical explanation that uses necessary long words scores badly. The number describes surface complexity, and it is genuinely useful for that as long as you do not mistake it for a measure of quality.

Reading the Output

Flesch Reading Ease           58.4    fairly difficult
Flesch-Kincaid Grade Level    10.2    tenth grade

Words                        1,240
Sentences                       71
Average sentence length       17.5 words
Average syllables per word     1.62

Longest sentence              48 words
Sentences over 30 words          6

The two headline scores are the least useful part of that output. The figures underneath are where the editing happens. Six sentences over thirty words in a 71-sentence article means roughly one in twelve is doing too much, and a single 48-word sentence is almost certainly two sentences that were joined by a comma.

Splitting those six sentences would move both scores without changing a single word of substance. That is the correct way to use the tool: find the specific sentences that drag the average, and fix those, rather than rewriting a whole page to hit a number.

What Score Should You Aim For

Whatever matches your reader. General consumer writing usually lands between grade 7 and grade 9. Trade and professional writing sits higher and should. Deliberately pushing a technical page down to grade 6 produces text that reads as condescending to the exact audience you want, and it does not help you rank, because reading level is not a ranking input.

What it does affect is whether people finish reading, and behaviour on the page is measurable. The reason to care about readability is that dense prose loses readers, not that a formula rewards you.

One caveat worth knowing: both formulas count syllables mechanically, so industry vocabulary inflates the score even when your audience reads those words fluently. If your subject requires four-syllable nouns, expect a higher grade level and do not treat it as a failure.

Questions