SMOG Index Calculator
SMOG readability grade for a pasted text, from polysyllable count, with the sample-size warning it needs.
What is SMOG Index?
SMOG — the Simple Measure of Gobbledygook — is the readability formula used most in health and patient-information work, because it is the one the published literature validated against comprehension tests rather than against school textbooks. It is read as the grade a reader needs to understand a text on a first reading, which is a slightly harsher bar than the other formulas set. Uniquely among the five, sentence length does not appear in it at all: difficulty is inferred entirely from how many three-syllable words the text uses.
How it works
The score is 1.043 times the square root of the polysyllable count scaled to a 30-sentence sample, plus 3.1291, which puts the result on the US grade system. The 30 is a sampling requirement from the original method rather than a constant of the language, and it is the reason SMOG is stable on whole documents and jumpy on a paragraph — so when the text has fewer than 30 sentences the tool says so and calls the figure an approximation of the standard formula rather than the formula itself. Polysyllables are counted with the category's shared syllable heuristic, which is where the unavoidable approximation enters.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.