SMOG Readability Calculator

SMOG stands for Simple Measure of Gobbledygook. It estimates the years of formal education a reader needs to fully understand a passage on the first reading. This calculator uses the precise conversion formula: grade = 1.0430 times the square root of (polysyllable count times 30 divided by sentences), plus 3.1291. It also shows McLaughlin's original shortcut, which is 3 plus the square root of the polysyllable count per 30 sentences.

A polysyllabic word has three or more syllables, such as "important" (3), "education" (4), or "vocabulary" (5). SMOG keys entirely on how many of these words appear relative to the number of sentences, because dense, multisyllabic vocabulary is what slows readers down most. Count every polysyllabic word in your sample, including repeats and proper nouns.

The classic SMOG method uses 30 sentences: 10 from the start of the document, 10 from the middle, and 10 from the end. Count the polysyllabic words across all 30 sentences and enter both totals. If your sample is not exactly 30 sentences, this calculator scales the polysyllable count to a 30-sentence basis automatically, so any sentence count from 1 up works.

SMOG was calibrated for 100 percent comprehension, meaning the reader understands everything in the passage. Formulas like Flesch-Kincaid target partial comprehension, often around 50 to 75 percent, so they tend to report a lower grade for the same text. That stricter target is why health and patient-education guidelines frequently recommend SMOG and ask for materials at a sixth to eighth grade level.

Many health-literacy guidelines suggest writing patient materials at a sixth to eighth grade SMOG level so the broadest audience can follow them. Shorter sentences and plainer words lower the grade quickly, since both reduce the polysyllable load per sentence. Aiming below grade 9 usually keeps content accessible to general readers.

No. This tool is for education and general readability estimation only, and it is not a substitute for professional advice on medical, legal, or accessibility compliance. SMOG is one signal among many, and the syllable-based heuristic can differ by a fraction of a grade from a hand count or a dictionary-based tool. Use the result as guidance and have a qualified reviewer confirm anything where accuracy is critical.