To calculate the SMOG reading grade level, begin with the entire written
work that is being assessed, and follow these four steps:
1. Count off 10 consecutive sentences near the beginning, in the middle,
and near the end of the text.
2. From this sample of 30 sentences, circle all of the words containing
three or more syllables (polysyllabic), including repetitions of the same
word, and total the number of words circled.
3. Estimate the square root of the total number of polysyllabic words
counted. This is done by finding the nearest perfect square, and taking
its square root.
4. Finally, add a constant of three to the square root. This number gives
the SMOG grade, or the reading grade level that a person must have reached
if he or she is to fully understand the text being assessed.
A few additional guidelines will help to clarify these directions:
A sentence is defined as a string of words punctuated with a period
an exclamation point (!) or a question mark (?).
Hyphenated words are considered as one word.
Numbers which are written out should also be considered, and if in
numeric form in the text, they should be pronounced to determine if they
Proper nouns, if polysyllabic, should be counted, too.
Abbreviations should be read as unabbreviated to determine if they are
Not all pamphlets, fact sheets, or other printed materials contain 30
sentences. To test a text that has fewer than 30 sentences:
1. Count all of the polysyllabic words in the text.
2. Count the number of sentences.
3. Find the average number of polysyllabic words per sentence as
Average= Total # of polysyllabic words/Total # of sentences
4. Multiply that average by the number of sentences short of 30.
5. Add that figure on to the total number of polysyllabic words.
6. Find the square root and add the constant of 3.
A quick version of the SMOG test:
Count the number of polysyllabic words in the chain of 30 sentences and
look up the approximate grade level on the SMOG conversion table.
SMOG Conversion Table
Total polysyllabic word counts
Approximate grade level (+/- 1.5 grades)
(Making Health Communication Programs Work, A Planner's Guide, US. Dept of
Health and Human Services, 1992)