Readability formulas are worth using and worth not trusting too far. Flesch Reading Ease and Flesch-Kincaid Grade Level both work from two measurable proxies — average sentence length and average syllables per word — and neither one has any idea what your sentences mean. A short sentence of dense jargon scores well; a long, elegantly constructed sentence of common words scores badly. Treated as a nudge toward shorter sentences and plainer vocabulary, they are useful. Treated as a target to optimise, they produce choppy prose that scores well and reads worse.
For general audiences, a Flesch-Kincaid grade around 8 is a reasonable aim, which is roughly where most newspapers sit. Technical documentation legitimately lands higher because the terminology is the point, and forcing it down means replacing precise words with vague ones.
Reading-time estimates rest on a similar approximation. Silent reading of ordinary prose runs somewhere around 200–250 words per minute for adult readers, and that is the range the word counter uses. Technical material with code samples, tables or formulas is read far more slowly and often non-linearly, so treat the estimate on a reference document as a floor rather than a prediction.
The Unicode text styler comes with a genuine accessibility warning that is rarely mentioned. Those "fonts" are not fonts — they are Mathematical Alphanumeric Symbols, a separate block of Unicode code points that merely resemble styled Latin letters. Screen readers handle them badly, announcing them character by character or skipping them entirely, and search engines do not treat them as equivalent to the letters they imitate. They are fine for a one-off decorative flourish. They should never be used in a name field, a heading, a link label, or anything that needs to be searchable, indexable or readable by assistive technology.
Reading the readability scores
The two scales run in opposite directions, which is a common source of confusion:
| Flesch Reading Ease | Flesch-Kincaid Grade | Reads like |
|---|---|---|
| 90–100 | 5th grade | Very easy — children's material |
| 60–70 | 8th–9th grade | Plain English — most journalism |
| 50–60 | 10th–12th grade | Fairly difficult — quality long-form |
| 30–50 | College | Difficult — academic and technical writing |
| 0–30 | Graduate | Very difficult — legal and specialist texts |