Clear Writing: How to Achieve and Measure Readability

THE WRITING CLINIC

What makes one piece of writing easy to read while another will cause readers' eyes to glaze over? The mysterious ingredient of good writing is a quality best described as readability. But how can a writer achieve readability? And is there a way of measuring it? Although certain computer programs offer a so-called readability measurement feature, wouldn’t it be nice to be able to check the readability of any piece of writing? To have a simple and completely portable yardstick for measuring reading ease? A way of quantitatively measuring readability? A way of making sure that what you have written is aimed at the intended audience?

Wait a minute! There is just such a formula: Robert Gunning’s largely forgotten “Fog Index.” It’s an easy-to-remember way of determining readability. In 1944, Gunning, a 36-year-old Ohio editor, quit his job and started a consulting business still not listed in the government’s index of occupations. The specialty of Robert Gunning Associates was counseling in clear writing—showing businesses how they could improve the readability of their communications.

Gunning’s clients included large corporations like the Standard Oil Co. and General Motors, United Press International, and newspapers such as the Louisville Courier-Journal, Hartford Courant, Washington Star, and Wall Street Journal, whose legendary editor Bernard Kilgore became a disciple. Gunning preached what most writers had long known—that certain factors played a part in readability: first and foremost, average sentence length in words, with the proportion of simple sentences, strong verb forms, familiar words, abstract words, long words and personal references all playing strong supporting roles.

Gunning's Readability Formula
Until that time, readability measurement had been the exclusive province of educators. But their formulas were complicated and required the laborious counting of certain not easily discerned factors. Many systems—even the highly touted yardsticks of readability guru Rudolph Flesch—employed four-decimal-place multipliers that were difficult to remember and gave a false sense of scientific accuracy.

Gunning discovered that only two qualities were critical to determining readability: the average number of words in sentences plus the percentage of “hard” words that might cause a reader to stumble. In his 1952 book, The Technique of Clear Writing, he described how to apply his innovative “Fog Index,” which is ideal for any kind of copy. It’s simple to calculate and easy to carry in your head.

1. Count the number of words in successive sentences. In a long piece, take several 100-word samples distributed evenly throughout. (Stop the sentence count with the sentence that ends nearest each 100-word total.) Divide the total number of words in each sample by the number of sentences. This yields the average sentence length of the copy.

2. Count the number of words of three syllables or more per 100 words. Don’t count proper names, word combinations of short words (i.e., bookkeeper, manpower, etc.) or three-syllable plural or past-tense verb forms as a result of adding -ed or -es (i.e., created or trespasses). This figure is the percentage of “hard” words in the copy.

3. Add these two numbers and multiply the result by 0.4.

This yields the Fog Index, which correlates exactly with school grade reading levels as determined by the McCall-Crabbs Standard Test Lessons in Reading. Thus, if your copy is addressed to a hypothetical audience with a fifth-grade educational level, the Fog Index of the tested copy should be no higher than 5.

The following table compares the Fog Index with reading levels by grade.

Fog Index Reading Level By Grade
17: College graduate
16: College senior
15 : College junior
14: College sophomore
13: College freshman
---------D A N G E R L I N E--------
12: High school senior
11: High school junior
---------EASY READING BELOW THIS LINE---------
10: High school sophomore
09: High school freshman
08: 8th grade
07: 7th grade
06: 6th grade
05: 5th grade

Cautions about Readability Measurements
A “sentence” in Gunning’s terms is not always the distance between a capital letter and a period, which makes it ideal for the punchy writing of direct mail copy. Units of thought (marked off by semicolons, colons, dashes or ellipsis points) are treated as sentences and so are independent clauses. An independent clause (sometimes called a main clause) is a group of words that make a complete statement, no matter what punctuation comes before or after. Such a clause can stand as a regular sentence, beginning with a capital letter and ending with a period. Or several independent clauses may be separated by semicolons or commas. (For example, J.N. Hook’s parody of Julius Caesar in his Guide to Good Writing contains three independent clauses: “She came, I saw, she conquered.”) What is a “word” sometimes causes trouble, too. In applying the Fog Index, we may define a word as anything with white space on either side of it.

If your copy tests 13 or more, you are beyond Gunning’s danger line of reading difficulty, and your readers are likely to find what you have written to be heavy going.

After measuring the readability of magazines, Gunning discovered a correlation between a magazine’s circulation and his Fog Index. Magazines with the highest mass appeal had the lowest average sentence length and the lowest percentage of difficult words.

Gunning also applied his formula to books and found a direct relationship between a low Fog Index and popularity. Still in print, Margaret Mitchell’s best-selling Gone with the Wind has a 6th grade reading level. Peyton Place also scores a 6. Mickey Spillane’s hard-boiled novels come in at 5, as do the works of Harold Robbins. J.D. Salinger, John Cheever and Truman Capote all average a Fog Index of 7, not markedly lower than Somerset Maugham, Sinclair Lewis or Ernest Hemingway. Harper Lee’s prize-winning novel To Kill a Mockingbird has a Fog Index of 5, which must account for its astonishing continuing sales in the millions and its presence on nearly every school reading list.

Applying his formula, Gunning gave English poet John Milton a Fog Index of 26. This was 11 points higher than Lincoln’s 269-word Gettysburg Address, which came in at 15. Gunning, who died in 1980, believed that 16 to 20 words was a good average word count for sentences in newspaper articles.

A low Fog Index for copy you have written is merely an assurance that the piece can be easily read by the widest audience—that readers of it will be induced to move along from one sentence to the next without stumbling and without excessive demands on their attention. The Fog Index cannot make you or anyone a great writer. Rather it is a measure of complexity in writing—for determining whether a piece of copy is geared to its intended audience. The Fog Index is a measuring tool, but only for use after you have written, not as a pattern before you write. “Good writing must be alive,” Gunning advised. “Don’t kill it with a system.”

Users of Robert Gunning’s Fog Index should recognize two things: First, reading ease isn’t only the ease of understanding words, phrases and sentences. There’s also the problem of how sentences relate to one another in a paragraph and how the paragraphs themselves relate. Any measure of word- or sentence-difficulty certainly correlates with overall reading difficulty, but it’s no exaggeration to say that there are writers who use simple words and write short sentences, yet whose copy isn’t a pleasure to read.

The Fog Index really is related to comprehensibility. It’s not necessarily about genuine readability—the property of copy that makes a reader want to keep on reading. Making something easier to read doesn’t always make it more interesting or more desirable to read. Using shorter sentences and simpler words indeed does yield copy comprehensible to a wider audience, but an increase in comprehensibility will not of itself make for greater readability.

It’s easy enough for writers to raise the comprehensibility of their copy by training themselves to write in short bursts and to choose less complicated words. Writing truly readable copy is quite another matter and less easily learned—you must cultivate an ear for the rhythms of the rich language that is English. Effective copy is not only clear and reads easily, but it also will sound right. In editing your copy (and it’s rare copy indeed that cannot be made better with one more revision), you should read not only for sense, but for euphony—the agreeableness of what you’ve written and its pleasurable effect on the ear (and thus on the eye). In short, try listening to your copy, even going so far as playing it back to yourself on a tape recorder.

A good writer takes the problem of writing seriously and attempts to marry comprehensibility and readability. It’s not easy to develop and maintain the skill of simple writing while at the same time keeping an ear open for the aptness of phrase and sentence. Only then will you succeed at the art that none of us will ever fully master—using the tools and the building blocks in the storehouse of language to create a deceptively simple structure of complex thoughts and emotions to entice readers and move them to action. The paradox is, of course, that if the simplicity is obvious, you have failed.