TextCheck

SMOG Index calculator

SMOG estimates the years of education needed to fully understand a text. It is widely used for health information.

Average grade level

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Paste at least a few sentences.

  • Words0
  • Sentences0
  • Syllables / word0.00
  • Words / sentence0.0
  • Complex words (3+ syllables)0%
Readability scores
FormulaScoreMeaning
Scores appear here as soon as you type.

See polysyllables drive SMOG

SMOG only counts words of three or more syllables. Swap them out and watch the grade fall.

Tap a highlighted word to swap it for a plainer one.

The will each and the to every . We that may be . Please us if you have questions.

SMOG index

14.6

  • Words28
  • Sentences3
  • Polysyllables (3+ syllables)12

1.043 × √(12 × 30/3) + 3.13

The SMOG formula

1.043 × √(polysyllables × 30 ÷ sentences) + 3.1291

G. Harry McLaughlin published SMOG (“Simple Measure of Gobbledygook”) in 1969. Polysyllables are words with three or more syllables. The formula was designed for samples of 30 sentences: ten from the start, middle and end of a text.

Why health writers use SMOG

SMOG was calibrated for complete comprehension rather than partial understanding, so it tends to give higher grades than other formulas. That conservative estimate is why many public-health bodies recommend it for patient materials, which are usually targeted at grade 6–8.

Tips to lower a SMOG grade

  • Replace medical or technical terms with everyday words where possible, and explain the ones you must keep.
  • Break long sentences, which reduces the density of polysyllables per sentence.
  • Use lists for steps and options.

Questions people ask

What does SMOG stand for?

Simple Measure of Gobbledygook, a name chosen by its creator, G. Harry McLaughlin, as a nod to Robert Gunning’s Fog index.

Can I use SMOG on short texts?

Yes, but results are less reliable under 30 sentences. The calculator scales your sentence count to 30, as the formula expects.

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