What does the SMOG Grade mean?

It estimates the U.S. school grade a reader needs to understand the text after a single reading. A SMOG Grade of 9 means an average ninth-grader should follow it, which is a common target for patient-facing health material.

What counts as a polysyllabic word?

Any word with three or more syllables. SMOG is driven entirely by how many such words appear, because longer words are a strong signal of harder text in English.

Why does SMOG ask for 30 sentences?

The original SMOG formula was calibrated on a sample of thirty sentences. With fewer than thirty, the tool normalises the polysyllable count to a thirty-sentence basis and labels the result as an estimate.

How does SMOG differ from Flesch-Kincaid?

Flesch-Kincaid blends sentence length and average syllables per word, while SMOG focuses purely on the count of polysyllabic words. SMOG is especially popular in healthcare because it targets the grade needed for full comprehension.

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No. All counting and scoring runs locally in your browser, so you can safely paste private or unpublished drafts.

English SMOG Readability Index

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The SMOG, or Simple Measure of Gobbledygook, grade estimates how hard a piece of English text is to read by counting its polysyllabic words. It is widely used in healthcare and public communication because it directly answers the question “what grade level can fully understand this on one reading?”

How it works

SMOG counts every word with three or more syllables — its polysyllables — across the text and relates that count to the number of sentences. The formula is:

SMOG Grade = 1.0430 × sqrt(polysyllables × (30 / sentences)) + 3.1291

When the text has about thirty sentences this is the exact SMOG score. For shorter passages the tool normalises the polysyllable count to a thirty-sentence basis and marks the result as an estimate. Syllables are counted with a vowel- group heuristic, the same practical approach used for other English readability measures.

Tips and example

A sentence such as “The nurse will check your blood pressure” has no three- syllable words and barely moves the score, while “The practitioner will evaluate your cardiovascular medication” is dense with polysyllables and pushes the grade up sharply. To lower a SMOG Grade, swap long words for short ones: “use” for “utilise”, “help” for “assistance”. For patient materials many health agencies aim for a SMOG Grade of around 6 to 8.