Rudolf Flesch

Chapter 2: Let's Start With the Formula

If you want to learn how to write Plain English, you must learn how to use a readability formula.

Of course this isn't true if you have a talent for writing. I've come across quite a few people who can write a booklet explaining an insurance policy simply because they have the knack. But I take it you're not blessed with that knack. You belong to the 98 or 99 percent of mankind who must learn Plain English the hard way. If so, you must know where you are and where you want to go. You need a yardstick, a measuring tool, something against which you can check your progress. That's what a formula is for.

There are by now dozens of readability formulas in existence, but for general use there are only a handful to choose from. They fall into two groups-those based on sentence length and a word list and those based, on sentence length and word length.

I worked out my own formula because I tried to apply the word list formulas to adult reading matter and got nowhere. So I went in a new direction and constructed a formula based on word length rather than a list. It was the first of this type and has become the most widely used formula in the country. There are other sentence and word length formulas, all of which are variations of mine. Their results aren't much different from my formula but, I think, mine is easier to use. So what you're going to get in this chapter is a mini-course in using the Flesch formula.

I developed the formula in the early 1940s. It measures the average sentence length in words and the average word length in syllables. You put these two numbers into an equation and get a number between 0 and 100 that shows you the difficulty of your piece of writing. If it's too hard to read for your audience, you shorten the words and sentences until you get the score you want.

At first blush you may think this is a very crude way of dealing with writing. Writing means conveying ideas from one mind to another. To use a mechanical gadget for this doesn't seem like an intelligent approach.

But wait a minute. I spent several years of my life doing the underlying research for this formula and got my Columbia University Ph.D. degree for it. I can assure you that it is based on some very complicated facts of human psychology. It works because it is based on the way the human mind works.

When you read a passage, your eyes and mind focus on successive points on the page. Each time this happens, you form a tentative judgment of what the words mean up to that point. Only when you get to a major punctuation mark-a period, a colon, a paragraph break-does your mind stop for a split second, sum up what it has taken in so far, and arrive at a final meaning of the sentence or paragraph. The longer the sentence, the more ideas your mind has to hold in suspense until its final decision on what all the words mean together. Longer sentences are more likely to be complex-more subordinate clauses, more prepositional phrases and so on. That means more mental work for the reader. So the longer a sentence, the harder it is to read.

Exactly the same thing is true of words. Some words are short and simple, others are long and complex. The complexity shows up in the prefixes and suffixes. Take is a simpie. short word that doesn't present much difficulty to a reader. But unmistakably has the prefixes un- and mis-and the suffixes -able and -ly and gives the mind much more to think about than take. (My very first readability formula was based on a count of prefixes and suffices to measure word complexity. A few years later I tried to make it easier to use and changed to a count of syllables. Statistically, the results are about the same.)

In using the formula, you count words and syllables to measure the mental work the reader will have to do. A paragraph that measures 0 on the scale is apt to give the reader a headache; a paragraph that scores 100 is child's play.

Let's take an example. Take the sentence "John loves Mary." That's short and sweet and obviously presents no reading difficulties. Its score is 92, which means "very easy."

Now let's say the same thing with a little more sophistication - "John has a profound affection for Mary." This adds some complexity to the idea. It rates "Plain English"-a score of 67-but gives the reader a little to think about. Just exactly what are John's feelings toward Mary?

Now let's go into further complexities: "Even though John is not normally given to a display of his deeper emotions, he allegedly has developed a profound affection for Mary, as compared to the more equable feelings he seems to have for Lucy, Fran and, to a lesser extent, Sue." This has a score of 32 ("difficult") and throws the whole affair into a state of some obscurity and ambivalence. The sentence now compares in difficulty with the Harvard Law Review.

All right, I've given you the fundamentals. Here's how you use the formula:

Test only the running text of your piece of writing. Skip titles, headings, subheads, section and paragraph numbers, captions, date lines and signature lines.

Step 1. Count the words.

Count the words in your piece of writing. Count as single words contractions, hyphenated words, abbreviations, figures, symbols and their combinations, e.g., wouldn't, full-length, TV, 17, &, $15, 7%.

Step 2. Count the syllables.

Count the syllables in your piece of writing. Count the syllables in words as they are pronounced. Count abbreviations, figures, symbols and their combinations as one-syllable words. If a word has two accepted pronunciations, use the one with fewer syllables. If in doubt, check a dictionary.

Step 3. Count the sentences.

Count the sentences in your piece of writing. Count as a sentence each full unit of speech marked off by a period, colon, semicolon, dash, question mark or exclamation point. Disregard paragraph breaks, colons, semicolons, dashes or initial capitals within a sentence. For instance, count the following as a single sentence:

You qualify if-

(1) You are at least 58 years old; and

(2) Your total household income is under $5,000.

Step 4. Figure the average number of syllables per word.

Divide the number of syllables by the number of words.

Step 5. Figure the average number of words per sentence.

Divide the number of words by the number of sentences.

Step 6. Find your readability score.

Find the average sentence length and word length of your piece of writing on the chart (below). Take a straightedge or ruler and connect the two figures. The intersection of the straightedge or ruler with the center column shows your readability score.


You can also use this formula: Multiply the average sentence length by 1.015. Multiply the average word length by 84.6. Add the two numbers. Subtract this sum from 206.835. The balance is your readability score.

The scale shows scores from 0 to 100. Zero means practically unreadable and 100 means extremely easy. The minimum score for Plain English is 60, or about 20 words per sentence and 11/2 syllables per word. Conversational English for consumers should score at least 80, or about 15 words per sentence and 1 1/2 syllables per word.

All Plain English examples in this book score at least 60.

Here are the scores of some reading materials I've tested. These are average scores of random samples.



Consumer ads in magazines


Movie Screen




Reader's Digest


Sports Illustrated


New York Daily News


Atlantic Monthly






Wall Street Journal


Harvard Business Review


New York Times


New York Review of Books


Harvard Law Review


Standard auto insurance policy


Internal Revenue Code

minus 6

Here's how the scores translate into school grades. Reading matter with the score shown on the left side will be easy for students on the level shown on the right.


School Level

90 to 100

5th grade

80 to 90

6th grade

70 to 80

7th grade

60 to 70

8th and 9th grade

50 to 60

10th to 12th grade (high school)

30 to 50


0 to 30

college graduate

Next, let me give you two important tips.

First, if you want to rewrite a passage to get a higher score, you'll have to cut the average sentence length. This means you'll have to break up long, complex sentences and change them to two, three or four shorter ones. In other words, sprinkle periods over your piece of writing. When you're turning subordinate clauses into independent sentences, you'll find that a lot of them will start with And, But or Or. Don't let that bother you. It's perfectly good English and has been good usage for many centuries. The Old Testament says, "And God said, Let there be light; and there was light." The New Testament says, "But Jesus gave him no answer." And Mark Twain wrote, "Man is the only animal that blushes. Or needs to." So never mind that old superstition. And don't-please don't-put unnecessary commas after your And's, But's and Or's.

Second tip: When it comes to replacing complex words with simple ones, take first aim at words with prefixes and suffixes, like establishment, available or required. Often the best Plain English replacement is a two-word combination like setting up, in stock or called for. If you can't think of a good substitute, use any good thesaurus or book of synonyms. You'll find that there's s no complex, legalistic word that can't be translated into Plain English.