Readability Test Tool

Quick and easy way to test the readability of your work.

Gunning Fog Index

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

In order to ensure that your writing resonates with your target audience, it’s important to understand the readability expectations of your audience and alter your writing to meet those expectations.

On this page, we’ll take a look at the Gunning Fog Index, a popular measure of readability. We’ll explain what the Gunning Fog Index is, how to calculate it, and why it’s important.

Want to know if your website meets the readability expectations of your audience? Keep reading to find out more.

What is the Gunning Fog Index?

Developed by American businessman, Robert Gunning, the Gunning Fog Index estimates the years of formal education needed to comprehend a passage of text on the first reading.

Gunning noticed that many high school students were unable to read, and he attributed this to a writing problem, believing that newspapers and business documents were full of complicated text.

He went on to become the first person to take readability research into the workplace, and he developed a consulting firm dedicated to readability. Gunning then worked with newspapers and popular magazines, helping writers and editors understand how to write to their target audience.

How to calculate Gunning Fog Index

To calculate the Gunning Fog Index, you need to take a passage of text at least 100 words and count the number of exact words and syllables. Then, divide the total number of words in the sample by the total number of sentences. This will give you the Average Sentence Length (ASL).

Next, you will need to count the number of words that contain three or more syllables that are not proper nouns, combinations of easy or hyphenated words, or two-syllable verbs made into three by adding -es and -ed endings. Then, you will need to divide that number by the total number of words in the sample passage. This will give you the Percent Hard Words (PHW).

Finally, you will need to add the ASL and PHW and multiply the result by 0.4.

Gunning Fog Index formula: Grade level= 0.4 (ASL + PHW).

What does my score mean?

The principle behind the Gunning Fog Index formula is that short sentences written in plain English receive a better score than longer sentences written in complex language.

A Gunning Fox Index score of 7 or 8 is ideal, and anything higher than 12 is too complex for most people to read.

Popular magazines, such as TIME and the Wall Street Journal average Gunning Fog scores of 11, while Shakespeare has a Gunning Fog Index of about 6.

Though considered a fairly accurate measure of readability, the Gunning Fog Index has some limitations. For instance, it doesn’t take into account that not all multi-syllable words are difficult.

Why does readability matter?

If you don’t meet the readability expectations of your website visitors, they will waste no time navigating away from your site.

In order to decrease bounce rates and keep people engaged with your content, you have to understand their readability expectations.

Are you writing for a medical publication? Or are you writing to elementary school kids? This will impact the complexity of your writing, and understanding your Gunning Fog score can help you alter your writing to meet the expectations of various audiences.

Want to improve your score?

Interested in learning more about your Gunning Fog Index score?

Check out our free readability test tool. You can simply enter your website URL, and we’ll calculate your score in a matter of seconds.

We also offer practical tips for improving your website's reach and readability.

Make sure your writing reaches the intended audience, and calculate your Gunning Fog Index score today.