Every readability tool quotes two numbers at you: a Flesch Reading Ease score and a Flesch-Kincaid grade level. One goes up as text gets easier, the other goes down, and both come from the same two measurements. Here's what the bands mean, what your genre should score, and the two levers that actually move the number.
Both formulas take a passage and compute exactly two things: average sentence length (words per sentence) and word difficulty (syllables per word). Flesch Reading Ease, published by Rudolf Flesch in 1948, maps them onto a 0-100 scale where higher is easier:
Reading Ease = 206.835 − 1.015 × (words/sentence) − 84.6 × (syllables/word)
Twenty-seven years later, J. Peter Kincaid adapted the math for the US Navy into a school-grade number, the version Word still shows in its readability statistics:
FK Grade = 0.39 × (words/sentence) + 11.8 × (syllables/word) − 15.59
Same inputs, different rulers. A Reading Ease of 65 and a grade level of 8.4 are two descriptions of the same prose.
| Reading Ease | Grade Level | What it feels like |
|---|---|---|
| 90-100 | 5th | Very easy; a bright 10-year-old cruises through it |
| 80-90 | 6th | Easy; digest magazines, popular fiction |
| 70-80 | 7th | Fairly easy; consumer magazines |
| 60-70 | 8th-9th | Plain English; newspapers, good web copy |
| 50-60 | 10th-12th | Fairly difficult; trade journals |
| 30-50 | College | Difficult; academic papers |
| 0-30 | College graduate | Very difficult; contracts, statutes, the worst of both |
Paste a passage, watch Reading Ease and grade level update live, with sentence and syllable counts.
Flesch-Kincaid Calculator →The honest answer is "whatever your reader reads at." Published approximations by genre: marketing copy and ads typically land at Reading Ease 70-90, news and general blogs at 60-70, technical documentation at 45-60, academic journal articles at 10-40, and legal contracts below 30. If you write a consumer blog scoring 35, the number is telling you something real. If you write a securities filing scoring 35, that's Tuesday.
Two famous reference points: insurance and government plain-language initiatives push forms toward 60+, and most style guides that quote a number (including plain-English movements in the UK and US) circle 60-70 as the general-audience band.
Take the classic: "The quick brown fox jumps over the lazy dog." Nine words, one sentence, eleven syllables. That's 9 words per sentence and 1.22 syllables per word. Reading Ease = 206.835 − 9.135 − 103.4 = 94.3, FK grade 2.3. Fifth grade, very easy.
Now: "Payment of the full balance remains due within thirty days of receipt, and late submissions may incur additional penalties pursuant to the applicable regulations." Twenty-four words in one sentence, forty-five syllables. Syllables per word climbs to 1.875, and Reading Ease falls to 206.835 − 24.36 − 158.63 = 23.9, FK grade 15.9. Both numbers came out of the same formula, and the 70-point swing matches exactly how different the sentences feel.
Run the before-and-after yourself on the readability calculator: paste a paragraph, note the score, cut the longest sentence in half, and rescore. The word counter and words-to-pages calculator cover the length side of the same edit; readability is the third leg of that stool.
60-70 on Flesch Reading Ease (about 8th-9th grade) for general-audience writing like blogs, newsletters, and most web copy. Marketing copy skews easier at 70-90, technical documentation sits near 45-60, and academic or legal writing legitimately lands at 30 or below. The score serves the reader, so pick the band your audience actually reads at.
They're two scalings of the same two inputs (words per sentence and syllables per word). Reading Ease runs 0-100 with higher meaning easier, published by Rudolf Flesch in 1948. The Grade Level version, adapted by J. Peter Kincaid for the US Navy in 1975, converts the same math into a US school grade like 8.4. Word shows both; most style guides quote Reading Ease.
Almost always syllables per word. Professional vocabulary (utilize, facilitate, approximately, implementation) runs 4-6 syllables each, and the formula weights that term heavily. A single 30-word sentence with five polysyllables can drag a whole paragraph's grade up by two levels. Split the sentence and swap two long words for short ones, then rescore.
It can be misleading. The formula measures sentence length and syllable density, nothing else: it can't detect jargon a reader knows, logical complexity, or whether a long sentence is well-built. A medical paper pitched at physicians should score 'difficult.' Use the score as a smoke test for unintended complexity, not as a quality grade.