The SMOG Readability Formula
Step 1: Take the entire text to be assessed.
Step 2: Count 10 sentences in a row near the beginning, 10 in the middle, and 10 in
the end for a total of 30 sentences.
Step 3: Count every word with three or more syllables in each group of sentences,
even if the same word appears more than once.
Step 4: Calculate the square root of the number arrived at in Step 3 and round it off
to nearest 10.
Step 4: Add 3 to the figure arrived at in Step 4 to know the SMOG Grade, i.e., the
reading grade that a person must have reached if he is to understand fully the text
assessed.
SMOG grade = 3 + Square Root of Polysyllable Count
The SMOG Formula is considered appropriate for secondary age (4th grade to
college level) readers.
The premises of McLaughlin’s SMOG Formula are:
1. A sentence is defined as a string of words punctuated with a period, an
exclamation mark, or a question mark.
2. Consider long sentences with a semi-colon as two sentences.
3. Words with hyphen are considered as a single word.
4. Proper nouns, if polysyllabic should be counted.
5. Numbers that are written should be counted. If written in numeric form,
they should be pronounced to determine if they are polysyllabic.
6. Abbreviations should be read as though unabbreviated to determine if they
are polysyllabic. However, abbreviations should be avoided unless commonly known.
7. If the text being graded is shorter than 30 sentences, follow the steps
below:
i. Count all the polysyllabic words in the text
ii. Count the number of sentences in the text.
iii. Divide the figures obtained in i. by the figure obtained in ii. to arrive at
Average Polysyllabic Words per sentence.
iv. Multiply the figure obtained in iii. with the average number of sentences
short of 30.
v. Add the figure obtained in iv. to the total number of polysyllabic words.
vi. Compare the number of polysyllabic words in the SMOG Conversion
Table.
| SMOG Conversion Table |
| Total Polysyllabic Word Count | Approximate Grade Level (+1.5 Grades) |
| 1 - 6 | 5 |
| 7 - 12 | 6 |
| 13 - 20 | 7 |
| 21 - 30 | 8 |
| 31 - 42 | 9 |
| 43 - 56 | 10 |
| 57 - 72 | 11 |
| 73 - 90 | 12 |
| 91 - 110 | 13 |
| 111 - 132 | 14 |
| 133 - 156 | 15 |
| 157 - 182 | 16 |
| 183 - 210 | 17 |
| 211 - 240 | 18 |
