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Published: December 6, 2022

What Is the SMOG Index?

Does your website meet the readability expectations of your target audience? In order to successfully reach people online, your website text needs to reflect the reading level of your target audience. Chances are pretty high that your content will be different if you’re writing to a group of doctors as opposed to high school students. On this page, we’ll take a look at the SMOG Index, what it means, and how you can improve the readability of your website.

What is the SMOG Index?

Created by G Harry McLaughlin, the SMOG Index estimates the years of education a person needs to comprehend a piece of writing, and it was created as an improvement of other readability formulas.

Though some believe SMOG is an acronym for Simple Measure of Gobbledygook, it is widely recognized to be a nod to Robert Gunning’s Fog Index.

To calculate the SMOG Index, you will need to take the entire passage of text being evaluated and select 10 sentences in a row near the beginning, 10 sentences in a row in the middle, and 10 sentences in a row near the end of the text.

Then, you will count every word with three or more syllables in each group of 10 sentences—even if the same word appears multiple times.

Next, you need to calculate the square root of the number derived in the previous step, and round it off to the nearest 10.

That number is your SMOG Index score.

What does my score mean?

The SMOG formula is generally accepted as appropriate for secondary age (4th grade to college) readers.

Unlike many other readability measures, which test for around 50-75% comprehension, McLaughlin used a 100% correct-score criterion.

Your SMOG Index score approximates the age needed to understand the text. And you can reference this chart for a breakdown of grade levels in the U.S.

  • 5-6 yrs. old — Kindergarten
  • 6-7 yrs. old — First Grade
  • 7-8 yrs. old — Second Grade
  • 8-9 yrs. old — Third Grade
  • 9-10 yrs. old — Fourth Grade
  • 10-11 yrs. old — Fifth Grade
  • 11-12 yrs. old — Sixth Grade
  • 12-13 yrs. old — Seventh Grade
  • 13-14 yrs. old — Eighth Grade
  • 14-15 yrs. old — Ninth Grade
  • 15-16 yrs. old — Tenth Grade
  • 16-17 yrs. old — Eleventh grade
  • 17-18 yrs. old — Twelfth grade
  • 18-22 yrs. old – College

Why does readability matter?

Did you know that the average American adult reads at the 7th to 9th grade level?

Understanding the readability expectations of your audience is important for attracting and maintaining the attention of your target audience online.

For example, are you writing to doctors or elementary school students? Chances are, your writing will vary pretty drastically depending on the audience to whom you’re writing.

In addition, it’s important to understand the intent of your readership.

People who are reading for recreation will likely be drawn to less complex passages than people conducting in-depth research on a particular topic.

By matching your text with the readability expectations of your audience, you can keep people on your website for longer periods of time and increase the likelihood that they will positively engage with your content.

Want to find out your score?

With our free readability test tool, you can simply enter the URL of your website and receive a detailed out of your readability scores and statistics.

We also offer some helpful tips and information to improve your website’s readability.

Make sure that your writing meets the expectations of your target audience. Try out our readability tool today!