Enter the total number of words, sentences, and complex words into the calculator to determine the Fog Index.

## Fog Index Formula

The following formula is used to calculate the Fog Index.

FI = 0.4 * ((words/sentences) + 100 * (complexWords/words))

Variables:
• FI is the Fog Index words is the total number of words in the text sentences is the total number of sentences in the text complexWords is the number of words in the text with three or more syllables

To calculate the Fog Index, divide the total number of words by the total number of sentences, then add to this the result of dividing the number of complex words by the total number of words and multiplying by 100. Multiply the final result by 0.4 to get the Fog Index.

## What is a Fog Index?

The Fog Index is a readability metric that indicates the number of years of formal education a reader would need to understand a piece of text on first reading. It considers factors such as the average sentence length and the percentage of complex words (those with three or more syllables) in the text. The higher the Fog Index score, the more complex the text is considered to be. This tool is often used by writers and editors to assess the readability of their work.

## How to Calculate Fog Index?

The following steps outline how to calculate the Fog Index.

1. First, determine the total number of words in the text.
2. Next, determine the total number of sentences in the text.
3. Next, determine the number of words in the text with three or more syllables.
4. Next, calculate the value of (words/sentences).
5. Next, calculate the value of (complexWords/words).
6. Next, multiply the value of (words/sentences) by 100.
7. Next, multiply the value of (complexWords/words) by 100.
8. Next, add the values obtained in step 6 and step 7.
9. Finally, multiply the sum obtained in step 8 by 0.4 to calculate the Fog Index.

Example Problem :

Use the following variables as an example problem to test your knowledge.

words = 500

sentences = 10

complexWords = 50