SMOG test of readability

SMOG test of readability

Every piece of writing and any text on your website must meet the readability expectations of your target audience. The SMOG index is an influential and popular writing tool that helps writers score their work for clarity of message and readability. The test comes from a clinical psychologist G. Harry McLaughlin who wanted to create a simple readability formula with the most reliable calculation. It was published in 1969 and is still used today. 

SMOG stands for ‘Simple Measure of Gobbledygook’. As a readability framework, this tool measures the years of education required by an average person to understand any piece of writing. SMOG test is best used when the length of the text consists of 30 sentences or more. 

How does the test work?

SMOG grade is the estimated years of education an average person needs to understand any piece of writing. To calculate the SMOG index you will need to take the entire passage of text consisting of 30 sentences being evaluated and select 10 sentences from the beginning, 10 from the middle row and 10 sentences at the end of the text. 

Next count every word with three or more syllables and square root the number rounding it to the nearest 10 and add three to the figure obtained.

The final figure is the reading level.

Source: The SMOG Index, Readable

The premises of the formula are:

  1. A sentence is a string of words that are punctuated with a period, an exclamation mark, or a question mark.
  2. Long sentences with semi-colon are considered as two sentences.
  3. Hyphen words are single words.
  4. Polysyllabic proper nouns should be counted.
  5. Written numbers should be counted and if they are in the numeric form they are pronounced to determine if they are polysyllabic.
  6. Abbreviations should be read as unabbreviated to determine if they are polysyllabic. But in most cases, abbreviations should be avoided.
  7. If the text is shorter than 30 sentences, follow the following steps;
  • Counting all polysyllabic words in the text
  • Counting all number of sentences
  • Divide the figure obtained in i. by the figure in ii. To arrive at average polysyllabic words per sentence.
  • Multiply the figure with the average number of sentences shorter than 30
  • Add the figure obtained to the total of polysyllabic words
  • Compare the number of polysyllabic words in the SMOG conversion table.

SMOG Conversion Table

Total Polysyllabic Word Count

Approximate Grade Level (+ 1.5 Grades)





























Why does readability matter?

To maintain the attention of your target audience online it is better to understand their readability expectations. Your writing greatly varies if you are addressing a doctor or elementary school students. It is good to understand the intent of your readership. The style of a reader and the purpose they are looking for in reading material is entirely different. The content readers look for varies with the purpose of their content research, at times the content required is less complex and to the point. Other times it may be a more complex research paper or in-depth analysis on a particular topic. Hence, readability develops within the purpose and use of the content displayed. Keeping up with the expectations of your audience you can expect them to spend more time on your website. This might increase the likelihood of your content engagement. 


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