Adapted from McLaughlin, G. (1969). SMOG grading: A new readability formula. Journal of Reading, 12 (8). 639-646.
The SMOG conversion tables were developed by Harold C. McGraw, Office of Educational Research, Baltimore Co. Public Schools, Towson, MD.
The SMOG Readability Formula is a simple method you can use to determine the reading level of your written materials. If a person reads at or above a grade level, they will understand 90-100% of the information. Generally, you need to aim for a reading level of sixth grade or less. In addition, to ensure that the text is clear and readable, read your draft aloud.
How to use the SMOG formula:
- Count 10 sentences in a row near the beginning of your material. Count 10 sentences in the middle. Count 10 sentences near the end. (30 total sentences)
- Count every word with three or more syllables in each group of sentences, even if the same word appears more than once.
- Add the total number of words counted. Use the SMOG Conversion Table I to find the grade level.
If your material has fewer than 30 sentences, follow the instructions for “SMOG on Shorter Passages” and use SMOG Conversion Table II.
Word Counting Rules:
• A sentence is any group of words ending with a period, exclamation point, or question mark.
• Words with hyphens count-as-one-word.
• Proper nouns are counted.
• Read numbers out loud to decide the number of syllables.
• In long sentences with colons or semicolons followed by a list, count each part of the list with the beginning phrase of the sentence as an individual sentence.
• Count abbreviations as the whole word they represent.
SMOG for Shorter Passages (< 30 sentences)
Use this formula and SMOG Conversion Table II for material containing less than 30 sentences, but not less than 10 sentences. - Count the total number of sentences in the material.
- Count the number of words with 3 or more syllables.
- Find the total number of sentences and the corresponding conversion number in SMOG Conversion Table II.
- Multiply the total number of words with 3 or more syllables by the conversion number. Use this number as the word count to find the correct grade level from Table I.
SMOG Conversion Table I
(for longer materials)
SMOG Conversion Table II
(use on material with < 30 sentences)
Word Count
Grade Level
of Sentences
Conversion #
0-2
4
29
1.03
3-6
5
28
1.07
7-12
6
27
1.1
13-20
7
26
1.15
21-30
8
25
1.2
31-42
9
24
1.25
43-56
10
23
1.3
57-72
11
22
1.36
73-90
12
21
1.43
91-110
13
20
1.5
111-132
14
19
1.58
133-156
15
18
1.67
157-182
16
17
1.76
183-210
17
16
1.87
211-240
18
15
2.0
14
2.14
13
2.3
12
2.5
11
2.7
10
3.0
Another Readability Option
The Flesch-Kincaid Grade Level Index
While the SMOG Readability Formula is an easy way to determine readability, another option is the Flesch-Kincaid Grade Level Index. This test is automatically calculated on your Microsoft Word documents. After Microsoft Word completes a grammar check (under tools in the tool bar), readability statistics are displayed.
One of the formulas that is similar to the SMOG formula is the Flesch-Kincaid formula. This index computes readability based on the average number of syllables per word and the average number of words per sentence. The score in this case indicates a grade-school level. For example, a score of 8.0 means that an eighth grader would understand the document. Standard writing approximately equates to the seventh- to eighth-grade level.