The readability formulas
Readability formulas estimate how easy a text is to read from countable features: sentence length, word length in letters or syllables, and the share of long words. They were developed for native readers, mostly in the United States, and grade levels refer to US school grades.
| Score | Based on | How to read it |
|---|---|---|
| Flesch Reading Ease | Words per sentence, syllables per word | 0–100; higher is easier. 60–70 is plain English |
| Flesch-Kincaid Grade | Same as Flesch, expressed as a grade | US school grade; 8 means a 13–14-year-old |
| Gunning Fog | Sentence length, words of 3+ syllables | Years of education needed; 12 is a high-school senior |
| SMOG | Words of 3+ syllables per 30 sentences | Grade level; often used for health information |
| Coleman-Liau | Letters per word, sentences per 100 words | Grade level; uses letters, not syllables |
| ARI | Characters per word, words per sentence | Grade level; also character-based |
Flesch Reading Ease score chart
| Score | Difficulty | Typical reader |
|---|---|---|
| 90–100 | Very easy | An average 11-year-old |
| 80–89 | Easy | Conversational English |
| 70–79 | Fairly easy | Popular fiction, readers aged 12–13 |
| 60–69 | Plain English | Most newspapers, readers aged 13–15 |
| 50–59 | Fairly difficult | High school seniors |
| 30–49 | Difficult | College level |
| 0–29 | Very difficult | University graduates, academic papers |
Readability scores and English learners
Readability formulas do not know which words are hard. Ubiquitous has four syllables and cat one, so the formulas get that right, but bow (to bend) and bow (a ribbon) look identical, and short rare words such as quell or wan count as easy. For learners, vocabulary is the bigger problem.
That is why Okuzeka's learner tools use word lists. To see the level of a text for an English learner, use the CEFR text level checker alongside these scores.
How to improve readability
- Split long sentences. Sentences over 25 words are highlighted in orange, over 35 in red. One idea per sentence is a good rule.
- Prefer common words. Use instead of utilize, help instead of facilitate.
- Use the active voice. The team found is shorter and clearer than it was found by the team.
- Cut filler. In order to → to; due to the fact that → because.
- Use lists and headings for steps and options instead of long paragraphs.
How sentences and syllables are counted
Sentences end at full stops, question marks and exclamation marks followed by a capital letter or a line break; common abbreviations such as Mr. and e.g. and decimal numbers are not treated as sentence ends. A blank line also ends a sentence, so headings count as short sentences.
Syllables are estimated with English spelling rules (vowel groups, silent e, -ed and -es endings). The estimate is within one syllable for most words, which is precise enough for the formulas.
