Readability Score Calculator

What this calculator does

Paste any piece of English writing - an article, email, blog post, or report - and this calculator scores how easy it is to read using five widely-used readability formulas:

• Flesch Reading Ease - a 0-100 score, higher means easier to read
• Flesch-Kincaid Grade Level - the US school grade needed to understand the text
• Gunning Fog Index - estimates years of formal education needed
• SMOG Index - commonly used for health and safety writing
• Coleman-Liau Index - based on characters instead of syllables
• Automated Readability Index (ARI) - another character-based estimate

It also gives you a checklist of practical, actionable recommendations.

Formulas Used

All formulas rely on three counts: words, sentences, and syllables (or characters).

Flesch Reading Ease:

$$206.835 - 1.015 \times \frac{words}{sentences} - 84.6 \times \frac{syllables}{words}$$

Flesch-Kincaid Grade Level:

$$0.39 \times \frac{words}{sentences} + 11.8 \times \frac{syllables}{words} - 15.59$$

Gunning Fog Index:

$$0.4 \times \left(\frac{words}{sentences} + 100 \times \frac{complexWords}{words}\right)$$

SMOG Index (complex words = 3+ syllables):

$$1.0430 \times \sqrt{complexWords \times \frac{30}{sentences}} + 3.1291$$

Coleman-Liau Index:

$$0.0588L - 0.296S - 15.8$$

Where L is average letters per 100 words and S is average sentences per 100 words.

Automated Readability Index:

$$4.71 \times \frac{characters}{words} + 0.5 \times \frac{words}{sentences} - 21.43$$

How to Use

1. Paste your text into the text box (English text works best - these formulas were designed for English).
2. Click Calculate.
3. Read the Flesch Reading Ease score and reading level.
4. Check the indices table for a second opinion from four other formulas.
5. Review the recommendations checklist for quick ways to simplify your writing.

Example

For a short paragraph with 120 words, 6 sentences, and 180 syllables:

$$\frac{words}{sentences} = \frac{120}{6} = 20$$ $$\frac{syllables}{words} = \frac{180}{120} = 1.5$$ $$FleschReadingEase = 206.835 - 1.015 \times 20 - 84.6 \times 1.5 = 59.8$$

A score of 59.8 falls in the "Fairly Difficult" range - roughly the reading level of a high-school student.

Notes

• These formulas were designed for English text; results on other languages are not meaningful.
• A longer sample (100+ words) gives a more reliable score than a single short sentence.
• No formula fully captures clarity - use this as a quick sanity check, not a strict rule.