Calculate Your Average Sentence Length

By Mark Nichol

Variety of sentence length is an important factor in good writing — attending to the number of words in each sentence enhances the rhythm of your composition — but careful writers occasionally monitor average sentence length, too.

There’s no reason to obsess about either factor, but check your numbers now and then. Although variety of sentence length occurs naturally, it’s a good idea, when it’s feasible, to recite your writing aloud to ensure that stacks of sentences of repetitively equal or nearly equal length aren’t slipping through. Note, however, that though striving for variety of length and attending to average length may seem contradictory practices, average length has nothing to do with consistent length.

And what’s the ideal average sentence length? It depends on the formality of your writing, and on your writing audience. Roughly, for a general audience, an ASL of less than 15 words is considered easy, 15 to 20 words is moderate, and more than 20 words is difficult.

I measured my posts from last week and discovered that they ranged in ASL score from 20.7 words to 33.9; the others were spaced fairly evenly within this range. I frequently employ colons to signal additional statements, and I didn’t count what follows the colons as separate sentences, but even if I did, the ASL for most of my posts would still likely be in the 20s. However, as I noted in my post about reading level, I assume that many Daily Writing Tips readers are above the norm in reading comprehension (though a sizeable number are English-language learners).

When I read about a study of ASL published in 1985, I learned that the ASL figures for leading American newspapers and magazines are comparable to the numbers for my posts. (Or they were comparable: The ASL for the best periodicals has probably declined in the last quarter-century.) But if I were writing for more modest general-interest publications, I would make an effort to reduce ASL to the low 20s or even the high teens.

Here’s a more complicated index called the fog factor: After determining the ASL, divide the number of words of three or more syllables by the total number of words. Add that number to the ASL. Multiply the sum by 0.4.

The number corresponds to reading-comprehension level corresponding to the number of years of education. For general-interest publications, the ideal total is between 7 and 9. The total for this post is over 14. Again, considering that it’s published on a blog about writing, that’s not excessive. However, if it inched any higher, or if the ASLs for my posts were routinely hitting in the upper 20s, I’d strive to simplify.

Clarity, construction, and correctness are the most important elements of good writing, of course, but conciseness is also a virtue.

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1 Response to “Calculate Your Average Sentence Length”

  • Roberta B.

    Good post! For most of us, the point of our writing is to be understood (rather than artistic!). I had a professor in college who said to aim for an ASL of 10 words or less which is way below college level. He said at the time most daily newspapers used that standard which was directed at the average reader. Maybe the demise of the daily and trend towards specialized publications have increased the ASL of written news to the 15 words stated above. I learned about the “fog index” (fog factor) in my second job from some papers left in the desk of my predecessor. It’s a little too cumbersome for my use. However, the principle is a good one – keep sentences shorter when using multi-syllable words. I found both to be good standards for reports that have some technical jargon or complex concept, especially when the audience consists of policymakers or average citizens.

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