Fog Index
The Fog Index is one measure of textual difficulty.
To calculate the Fog Index of the passage, do the following:
- Count the number of words in the paragraph, W.
- Count the number of sentences in the paragraph, S.
- Count the number of hard words of three syllables or more, HW.
- Apply the following formula: (W/S + HW/Wx100)x0.4
The Fog Index gives the number of years of education that the reader needs to understand the paragraph. Typically, in technical documentation, aim for the Fog Index between 10 and 15. The Fog Index formula implies that short sentences written in plain English achieve the better score than long sentences written in complicated language.