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7. The Fog Index
This is an ‘old’ way of measuring just how clear your writing is, this days some
word processing packages will do this for you. Most of us think we write clearly,
but that is often because we have become too close to our own style, and we
have learnt to understand it. Other people may not find it quite so easy to read.
That is where the fog index comes in. Although it does not account for your
actual choice of words and whether they are appropriate to the situation or
not, it does cover two important factors which have a major impact on
understanding: word length and sentence length. By calculating this index, you
may assess how clearly you are putting across your message. The calculation
process is shown in Figure 6. Of course you don’t need to go through this
tedious process any more as your word processing programme may do this for
you.

Figure 6: The Fog Index

STEP 1

Count the number of words in the passage. Count the number of
sentences. Then divide the number of words by the number of sentences.

STEP 2

Count the number of words with three syllables or more (you can discount
necessary technical terms or names).

STEP 3

Divide the number of words with three or more syllables by the total
number of words in the passage. Then multiply by 100.

STEP 4

Add the result of Step 1 to the result of Step 3 This gives you the FOG
INDEX.

Under 30 Probably gets the message over
30 ‐40 Not easy to read
Over 40 Gobbledegook

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