HesapHanem

SMOG Index Calculator

Estimate the years of education needed to understand your text.

How it is calculated

The tool counts sentences and words with three or more syllables (polysyllables), then applies grade = 1.0430 × √(polysyllables × 30 ÷ sentences) + 3.1291. The factor 30 ÷ sentences scales the count up or down to a 30-sentence sample, which is what the original SMOG method assumes.

Syllables are estimated from the spelling: each run of the vowels a, e, i, o, u, y counts as one, minus one for a final silent e. Only the letters a to z are looked at, so the tool is meant for English text; accented letters and digits are ignored. A sentence is counted for every run of ., ! or ?, so abbreviations such as Dr. and decimals such as 3.5 each add a sentence. The estimate often overcounts words like every or minutes, and short samples give rough results.

Worked example

The sample is four sentences: Regular exercise improves cardiovascular health. Doctors recommend moderate activity for thirty minutes every day. Before beginning any unfamiliar program, consult a physician about potential complications. Gradually increasing intensity prevents unnecessary injuries.

The tool finds 4 sentences and 19 words judged to have three or more syllables. Scaled to 30 sentences: 19 × 30 ÷ 4 = 142.5. Square root: 11.94. Grade: 1.0430 × 11.94 + 3.1291 = 15.58, which means a reader needs roughly university-level schooling for this text.

Try this example →

Common mistakes

  • Pasting a very short passage and treating the grade as exact. SMOG is built for about 30 sentences, and a few sentences make the result jump around.
  • Pasting text in a language other than English. Only the letters a to z are examined, so the syllable count is meaningless for Turkish, German and other languages.
  • Leaving in headings, bullet labels, dates or abbreviations such as Dr. and e.g. Each full stop is counted as a sentence end, which lowers the grade.
  • Reading 15.58 as an age. It is a school grade level, not an age.
  • Rewriting purely to lower the number, for instance by chopping sentences. Splitting sentences lowers the score without necessarily making the text clearer.

About this calculator

This calculator finds the SMOG readability grade (Simple Measure of Gobbledygook) of English text: grade = 1.0430 × √(polysyllabic word count × (30 / sentence count)) + 3.1291, using words of three or more syllables as the main signal of reading difficulty. The result is expressed as a US school grade level, i.e. the years of education needed to fully understand the text on first read.

Healthcare communicators, educators, and technical writers use SMOG — recommended by health-literacy guidelines for patient materials — to check that instructions, consent forms, and public information are written at an accessible reading level.

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Comments (1)

  • Editorial team

    Sentences are counted from the full stops, question marks and exclamation marks in the text, so abbreviations like Dr. and decimals like 3.5 each count as a sentence end and pull the grade down. A heading without punctuation merges into the next sentence. Before relying on the grade, check the sentence count the tool reports and tidy the text. If a grade looks off, post the polysyllable and sentence counts it showed.

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