SMOG Readability Calculator
Calculate the SMOG grade of your text from polysyllabic words and sentence count. The standard for health content — free and 100% in-browser.
What is the SMOG Readability Calculator?
The SMOG index (Simple Measure of Gobbledygook) estimates the US school grade a reader needs to fully understand your text.
- Exact SMOG formula: 1.0430 × √(polysyllables × 30 ÷ sentences) + 3.1291
- Automatic warning when the text is under the validated 30-sentence sample
- Full list of polysyllabic words with counts
- Live word, sentence and polysyllable stats
- Runs entirely offline in your browser
How to use the SMOG Readability Calculator
- 1
Paste your text — ideally 30 sentences or more — into the box.
- 2
Read the SMOG grade in the stats grid.
- 3
Check the polysyllabic-word chips to see which words drive the score.
- 4
Replace long words with shorter ones and watch the grade drop live.
About the SMOG Readability Calculator
The SMOG index (Simple Measure of Gobbledygook) estimates the US school grade a reader needs to fully understand your text. This calculator applies McLaughlin's 1969 formula — 1.0430 × √(polysyllables × 30 ÷ sentences) + 3.1291 — and lists every three-plus-syllable word that contributed to the score.
SMOG is the readability measure most often required for healthcare and patient-education material, because it was validated against 100% comprehension rather than partial understanding. Health writers typically aim for a SMOG grade of 8 or below. The formula was normed on 30-sentence samples, so this tool warns you when your text is shorter and the grade is less reliable.
Analysis happens 100% locally in your browser — nothing you paste is ever uploaded, which matters when you are checking unpublished or sensitive health copy.
Frequently asked questions
What is a good SMOG score?
For general audiences, grade 8 or below is the common target — it is the level most public-health style guides require for patient materials. News writing typically lands around grade 9–12, and academic text higher.
Why does SMOG want 30 sentences?
McLaughlin validated the formula on samples of 30 sentences (10 from the start, middle and end of a document). With fewer sentences the square-root scaling still computes a grade, but the estimate gets noisy — this tool shows a warning in that case rather than hiding it.
How is SMOG different from Flesch-Kincaid?
SMOG only counts words of three or more syllables and calibrates for full comprehension, so it usually reports one to two grades higher than Flesch–Kincaid on the same text. That is by design — it is the more conservative measure, which is why health literacy work prefers it.
How are polysyllabic words counted?
Every word with three or more syllables counts, including repeats and proper nouns, per the original method. Syllables are estimated with the standard vowel-group heuristic, so a handful of unusual words may be counted one syllable off.
Is my text stored or uploaded?
No. The calculation runs in your browser with JavaScript; your text never leaves your device and the tool works offline.
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