Readability Index Calculator
Calculate readability index easily with our free tool. Get practical results, tips, and comparisons for everyday decisions.
Formula
Flesch Ease = 206.835 − 1.015 × (words/sentences) − 84.6 × (syllables/words)
The Flesch Reading Ease score is computed from average sentence length and average syllables per word. The Flesch-Kincaid Grade Level, Gunning Fog, and SMOG use similar inputs but different coefficients to estimate the school grade level required for comprehension.
Worked Examples
Example 1: Simple Web Content
Problem: Analyze: 'The cat sat on the mat. It was a warm day. The sun was bright and the sky was blue. The cat liked to nap in the sun.'
Solution: Words: 30 | Sentences: 4 | Avg words/sentence: 7.5\nAvg syllables/word: 1.07\nFlesch Ease: 206.835 - 1.015(7.5) - 84.6(1.07) = 108.8 → capped at 100\nFK Grade: 0.39(7.5) + 11.8(1.07) - 15.59 = 0.0
Result: Flesch Ease: 100 (Very Easy) | FK Grade: ~1 | Elementary level
Example 2: Academic Text Analysis
Problem: Analyze a passage with 200 words, 8 sentences, avg 25 words per sentence, avg 1.8 syllables per word, and 40 polysyllabic words.
Solution: Flesch Ease: 206.835 - 1.015(25) - 84.6(1.8) = 28.9\nFK Grade: 0.39(25) + 11.8(1.8) - 15.59 = 15.6\nGunning Fog: 0.4 × (25 + 20) = 18.0\nSMOG: 1.043 × √(40 × 30/8) + 3.13 = 15.9
Result: Flesch Ease: 28.9 (Difficult) | FK Grade: 15.6 | Graduate level
Frequently Asked Questions
What is the Gunning Fog Index?
The Gunning Fog Index estimates years of formal education needed to understand text on first reading. It considers sentence length and percentage of complex words (3+ syllables). A Fog Index of 12 requires college-level reading ability. Ideal business writing scores 8-10. Texts scoring above 17 are extremely difficult for general audiences.
What is the SMOG Index?
SMOG (Simple Measure of Gobbledygook) predicts the grade level needed to comprehend a text. It focuses specifically on polysyllabic words (3+ syllables) and is considered one of the most accurate readability formulas for health-related materials. SMOG typically gives scores 1-2 grades higher than other formulas for the same text.
What readability score should I target?
For general audiences, aim for a Flesch Reading Ease of 60-70 (Flesch-Kincaid grade 7-8). For web content, grade 6-8 works best. For academic papers, grade 12+ is acceptable. For health communications, the CDC recommends grade 6-8. For legal or technical documents, grade 10-12 is typical. Always consider your specific audience's reading level.
What is the Flesch-Kincaid readability score?
The Flesch-Kincaid Reading Ease score (0–100) measures how easy text is to read — higher scores mean easier reading. The grade-level variant estimates the US school grade needed to understand the text. Scores are calculated from average sentence length and average syllables per word. General audiences need a score of 60–70 (8th–9th grade level).
How do I improve the readability score of my writing?
To improve readability: use shorter sentences (aim for 15–20 words average), choose simpler words (use 'use' not 'utilize'), break up long paragraphs, use subheadings and bullet points, avoid jargon unless writing for specialists, and use active voice. Hemingway App and similar tools provide real-time readability feedback as you write.
What is the Gunning Fog Index for text complexity?
The Gunning Fog Index estimates years of formal education needed to understand text on first reading. Formula: 0.4 × [(words/sentences) + 100 × (complex words/words)], where complex words have 3+ syllables. A score of 12 targets high school graduates; 17 targets college graduates. Most accessible writing scores between 7 and 12.