Readability Scores Explained: Flesch–Kincaid and Friends

Readability formulas estimate how much schooling a reader needs to understand a passage on the first read. They're used everywhere from journalism to UX writing to keep prose clear — and clearer content tends to convert and rank better too.

The two things every formula measures

Almost all readability formulas boil down to two inputs:

1. Sentence length — words per sentence.
2. Word complexity — syllables per word (or the share of long words).

Shorter sentences and simpler words score easier. That's it.

Reading the scores

• Flesch Reading Ease — a 0–100 score where higher is easier. 90+ is very easy; 60–70 is standard (roughly 8th–9th grade, a good target for general audiences); below 30 is very difficult.
• Flesch–Kincaid Grade Level — estimates the US school grade needed. Aim for grade 7–9 for broad audiences.
• Gunning Fog Index — similar grade estimate, weighted by the share of complex (3+ syllable) words.

How to improve a score

• Split long sentences in two.
• Prefer short, common words over jargon where the meaning survives.
• Cut filler ("in order to" → "to").

Note the goal isn't to write for children — it's to remove unnecessary difficulty so your actual ideas come through.

Measure it

Paste a draft into the Readability Score tool to see its Flesch Reading Ease, Flesch–Kincaid grade, and Gunning Fog index side by side, along with the word, sentence, and syllable counts driving them. Compare a rewrite to watch the score climb as you simplify.