Text Readability Checker

How readability scores are calculated

Readability formulas use two basic measurements: average sentence length and syllable count per word. The Flesch-Kincaid Reading Ease formula is: 206.835 − 1.015 × (total words ÷ total sentences) − 84.6 × (total syllables ÷ total words). The result is a 0–100 score where higher values mean easier reading.

The Grade Level converts the same inputs to a US school grade: 0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59. The Gunning Fog Index counts complex words (3+ syllables) as 0.4 × ((words ÷ sentences) + 100 × (complex words ÷ words)). The SMOG Index uses 1.0430 × √(30 × complex words ÷ sentences) + 3.1291. Syllables are estimated by counting vowel groups.

Reading ease score ranges

Flesch-Kincaid Reading Ease scores and their interpretations.

How to use the Readability Checker

What is readability

Readability measures how easy a text is to read and understand. It considers factors like sentence length, syllable count, and word complexity. Readability scores help writers ensure their content matches the reading ability of their target audience.

Different formulas explained

The Flesch-Kincaid Reading Ease scores text from 0 (very difficult) to 100 (very easy) based on syllables per word and words per sentence. The Grade Level formula converts this to a US school grade. Gunning Fog focuses on complex words (3+ syllables). SMOG is particularly accurate for health and technical content.

Target scores by audience

For general web content, target a Flesch-Kincaid Reading Ease of 60-70 and Grade Level 8-9. Marketing copy benefits from 70-80. Academic content falls at 30-50. Legal documents typically score below 30. Understanding your audience is key to choosing the right target.

Limitations and considerations of readability formulas

Readability formulas are powerful tools, but they have important limitations that every user should understand. The most significant limitation is that these formulas measure only surface-level text features — sentence length and syllable count — and do not evaluate meaning, coherence, clarity, or organization. A text with short sentences and simple words can still be confusing if the ideas are poorly structured, and conversely, a well-organized text with some longer sentences can be perfectly readable.

Readability scores are also language-dependent. All major formulas were developed for English text and may not transfer well to other languages. Spanish, French, and German have different syllable patterns and sentence structures that can produce misleading scores. Some languages have their own adapted readability formulas, but these are less common and less standardized than the English-based ones that our checker uses.

Another consideration is that readability formulas do not account for domain-specific vocabulary. Technical terms that are familiar to a specialist audience may be marked as "complex" by the formula because they have multiple syllables, but they are perfectly appropriate for that audience. The SMOG and Gunning Fog indices are particularly sensitive to this, as they heavily weigh polysyllabic words regardless of context or audience familiarity with the terminology.

Finally, readability scores should be used as guidelines, not absolute rules. A Flesch-Kincaid score of 55 might be perfectly appropriate for a quality magazine article aimed at educated adults, even though the formula labels it "fairly difficult." The best approach is to use readability scores as one input in your writing process, combined with human judgment about your specific audience, purpose, and context. No formula can replace a thoughtful editor.

Frequently asked questions