 How To Write Well:
Section 9 - The Fog Test
Contents: The Fog Test
If you would like to test a piece of your own writing for clarity, then try this Fog Test!
THE FOG TEST:
This test was invented by an American, Robert Gunning, as a yardstick to measure how readable a piece of writing might be.
Measuring the amount of mental fog in a piece of writing is not an exact science, so you can't expect a score produced by this test to be anything more than a rough indication of how difficult the writing will be to read. But the score will at least be an objective thing, and with practice you will be able to apply the test very quickly.
If the document is a short one, test the whole of it. If it is a long one, a test of short passages selected at random will be enough.
To get the score!
1. Find the average sentence length. In the margin, jot down the number of words in each sentence in the passage. Assume that a colon or semicolon makes a fresh sentence. At the bottom of the page, add the total number of words. Divide this total by the number of sentences to get the average number of words to the sentence.
2. Find the percentage of long words.
Go through the same piece of writing, ticking off each word that has three syllables or more when spoken. But do NOT tick any long words that:
(a) Begin with a capital letter such as the name of a person, place, body etc, e.g., 'Robinson', 'Manchester', 'Maintenance Department', 'September'.
(b) Are made up of short words run together, e.g., 'however', 'understanding', 'waterproof'.
(c) End with '_ed' as a third syllable, e.g., 'reported', 'protected', 'supported'.
Count the total number of long words you have ticked, Then work out the percentage they represent of the total number of words in the passage (which you know from step 1).
Number of long words x 100 = percentage of long words
Total number of words 1
3. Add the figure you get from step 1 to the one you get from step 2. The result is the "FOG Index" of the writing.
To evaluate the score:
Check the fog index figure against this scale:
Above 40:
Almost unreadable for most readers. They may think they have understood it, but a comprehension test would probably show that they have taken very little in.
35 - 40
Very heavy reading. Just about acceptable if it's technical stuff for a technician - but there are probably a lot of unnecessary abstractions and complex sentences.
30 - 35
Moderately heavy reading. Acceptable for many Research and Development reports and for an occasional report to senior management on a highly complex subject. But this is too high for normal paperwork. (This is the norm for 'Times' and 'Guardian' leaders.)
25 - 30
Fairly easy reading. About right for most paperwork passing between managers and staff. But still too high a score for sales writing or messages on the notice board. (This is the norm for 'Express' and 'Mail' leaders.)
20 - 25
Easy reading. This is the range for personal writing such as business letters, for hard-hitting selling copy or for notices to be read by all levels in the company. (This is the norm for 'Mirror' and 'Sun' leaders.)
Below 20
Very easy reading. If you can get your ideas over as simply as this, you are in some good company. A lot of great literature scores less than 20 (for instance Antony's "Friends, Romans, countrymen" speech scores 17, the opening of the story of the creation in Genesis scores 15.)
Comments and feedback on this guide are most welcome.
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