SMOG Readability Calculator

Calculate SMOG grade level using the Simple Measure of Gobbledygook formula. Preferred for healthcare and patient education materials. Counts polysyllabic words and applies McLaughlin's 1969 formula.

SMOG Grade Level
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Polysyllabic Words (3+ syllables) —
Sentences Analyzed —
Reading Audience —
Extended More scenarios, charts & detailed breakdown ▾
SMOG Grade Level
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Polysyllabic Words —
Sentences —
Accuracy Note —
Professional Full parameters & maximum detail ▾

SMOG Score

SMOG Grade Level —
FK Grade Level (comparison) —

Text Complexity

Polysyllabic Words (3+ syllables) —
Polysyllabic Word % —
Sentence Count —
Word Count —

CDC Plain Language Check

CDC Plain Language Target (≤ 8th grade) —

How to Use This Calculator

  1. Paste your text into the Input Text field.
  2. For most accurate results, use 30 or more sentences.
  3. The calculator counts polysyllabic words (3+ syllables) and computes the SMOG grade level.
  4. Use the Compare to FK tab to see SMOG alongside Flesch-Kincaid scores.
  5. Check the Professional tier for CDC Plain Language compliance check.

Formula

SMOG Grade Level = 1.0430 × √(Polysyllabic Words × (30 ÷ Sentence Count)) + 3.1291

Where polysyllabic words = words with 3 or more syllables. Best accuracy requires 30+ sentences.

Example

Text with 30 sentences and 20 polysyllabic words: SMOG = 1.0430 × √(20 × (30/30)) + 3.1291 = 1.0430 × 4.472 + 3.1291 = 7.8 (8th grade — meets CDC plain language target).

Frequently Asked Questions

  • SMOG (Simple Measure of Gobbledygook) was developed by G. Harry McLaughlin in 1969. The formula is: Grade Level = 1.0430 × √(Polysyllabic Words × (30 ÷ Sentences)) + 3.1291. A polysyllabic word has 3 or more syllables. The formula is most accurate with 30 or more sentences.
  • SMOG gives more conservative (higher) grade level estimates than Flesch-Kincaid, making it safer for health communication. The CDC, NIH, and Joint Commission recommend SMOG for patient education materials. Research shows patients need to understand health materials at their actual reading level — overestimating difficulty is safer than underestimating it.
  • The CDC "Simply Put" guide recommends healthcare materials be written at the 6th–8th grade level (SMOG ≤ 8). The American Medical Association recommends below 6th grade for patient handouts. Studies show the average American adult reads at the 8th grade level.
  • SMOG typically scores 2–4 grade levels higher than Flesch-Kincaid for the same text. FK uses average syllables per word, which dilutes the impact of complex polysyllabic words. SMOG counts only polysyllabic words (3+ syllables), which more directly measures the vocabulary complexity that challenges readers.
  • The original SMOG formula requires exactly 30 sentences — 10 from the beginning, 10 from the middle, and 10 from the end of a document. This calculator adjusts the formula proportionally for shorter texts, but results are most accurate with 30+ sentences. For texts under 15 sentences, treat results as approximate.

Related Calculators

📚 Flesch-Kincaid Calculator 📖 Readability Calculator 🎤 Speech Time Calculator 📊 Word Frequency Counter
Sources & References (5) ▾
  1. McLaughlin (1969) — SMOG Grading: A New Readability Formula — Journal of Reading / G. Harry McLaughlin
  2. CDC "Simply Put" Health Communication Guide — Centers for Disease Control and Prevention
  3. NIH Plain Language Guidelines — National Institutes of Health
  4. Joint Commission — Health Literacy Standards — The Joint Commission
  5. American Medical Association — Health Literacy Manual — American Medical Association