The Flesch-Kincaid readability tests estimate how hard a piece of English text is to read. They are widely used in journalism, government plain-language guidelines, and content marketing because they turn a fuzzy idea — “is this easy to read?” — into two concrete numbers from only three inputs.
How it works
Both formulas use total words, total sentences, and total syllables. Define average sentence length as words divided by sentences, and average word length as syllables divided by words. The two scores are then:
Reading Ease = 206.835 − 1.015 × (words/sentences) − 84.6 × (syllables/words)
Grade Level = 0.39 × (words/sentences) + 11.8 × (syllables/words) − 15.59Reading Ease runs roughly from 0 (very hard) to 100 (very easy); Grade Level maps onto U.S. school grades. Syllables are estimated by counting vowel groups in each word after stripping common silent endings, which is the standard practical approximation for English.
Understanding the Reading Ease score
| Score range | Difficulty | Typical context |
|---|---|---|
| 90–100 | Very easy | Children’s picture books |
| 70–90 | Easy | Conversational content, consumer apps |
| 60–70 | Standard | General web copy, news articles |
| 50–60 | Fairly difficult | Technical documentation |
| 30–50 | Difficult | Academic papers |
| 0–30 | Very difficult | Legal documents, specialist journals |
Most plain-language guidelines aim for 60 or higher. The US government’s plain-language mandate and many insurance disclosure rules target a Grade Level of 8 or below.
Worked example
Consider two sentences:
Easy: “Click Save when you are done. The file will update.” — Two short sentences, all single-syllable words, Reading Ease near 100, Grade Level near 1.
Hard: “Notwithstanding the aforementioned obligations, any implementation of the aforementioned contractual provisions shall necessitate verification of regulatory compliance.” — One long sentence with multi-syllable words like notwithstanding (5 syllables) and aforementioned (5 syllables), Reading Ease near 0, Grade Level near 20.
The contrast shows how dramatically sentence splitting and word choice move the scores.
What to change to improve your score
Sentence length matters most. The Reading Ease formula weights sentence length at 1.015 per word-per-sentence. A single 40-word sentence is harder than two 20-word sentences, even if all the words stay identical. Split complex sentences first.
Then simplify long words. The formula weights syllables-per-word at 84.6 — the heaviest coefficient. Replacing utilise (3 syllables) with use (1 syllable) and approximately (5 syllables) with about (2 syllables) each move the score noticeably.
Do not chase the number blindly. Some technical topics genuinely require precise vocabulary. If your audience is specialists, a Grade Level of 12 may be entirely appropriate. Readability scores are a diagnostic tool, not an instruction to replace every long word with a short one.
The tool recalculates as you type, so you can make one change at a time and watch the score respond in real time. Everything runs locally in your browser — nothing is uploaded.