SMOG estimates the years of education needed to understand text. Widely used in healthcare communication.
Use SMOG whenever you are writing for health and medical audiences. The National Institutes of Health, the CDC, and most patient-education guidelines recommend SMOG specifically because it correlates with 100% comprehension rather than approximate understanding — critical when readers must follow instructions exactly.
SMOG is the strictest of the polysyllable-based formulas; expect SMOG to land 1–2 grade levels above Flesch–Kincaid on the same text. Compared to Dale–Chall, SMOG ignores familiarity (treats "everyone" and "epistemology" similarly) but is far simpler to compute.
SMOG (Simple Measure of Gobbledygook) was created by G. Harry McLaughlin in 1969 and is the most widely used readability formula for health communication.
The score is the years of education needed to comprehend the text. SMOG 7 means a typical 7th grader should understand it.
Unlike Flesch-Kincaid, SMOG is calibrated for 100% comprehension rather than approximate understanding.
SMOG correlates strongly with comprehension among adults reading medical material. It is the recommended formula by the National Institutes of Health (NIH) for evaluating patient education materials.
The original formula expects exactly 30 sentences. This tool scales the polysyllable count proportionally when your text is longer or shorter.
For consumer health communication, aim for SMOG 6–8.
Input
Patients experiencing persistent symptoms should consult their physician immediately for evaluation.
Output
SMOG Index: 14.2 — College level.
Five polysyllabic words ("experiencing", "persistent", "symptoms", "physician", "immediately", "evaluation") drive the SMOG estimate. SMOG uses √polysyllables, so a few extra long words have a noticeable but bounded effect.
Classic 0–100 readability score.
readabilityU.S. grade level for your text.
readabilityPenalises complex (3+ syllable) words.
readabilityNo syllables needed — just characters.