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Readability Statistics

Readability tests are a measure of the ease of comprehension of a written text. The results are obtained solely through the analysis of word and sentence characteristics of the subject text and do not have the benefit of an actual statistical survey of human readers.

Typical characteristics used in the analysis include number of words, number of syllables per word, sentence length, and number of sentences. The test may also compare words found within the subject text to a list of “common” words.


Information shown in the analysis sidebar


New Dale Chall

The Dale Chall formula was created by Professor Edgar Dale and Jeanne S. Chall (who actually founded the Harvard Reading Lab), and focuses mainly on sentence length and uncommon, or difficult words. This leads to a final “grade” score that tells us which level of education and individual might be expected to have in order to fully comprehend the text.

Most readability formulas were actually developed with education in mind – for scholastic textbooks, where simple communication of key points is crucial.

But that doesn’t mean they’re only good for textbooks – readability itself is a universal concept, because people simply aren’t going to pay attention to, or feel involved in, writing that they find impenetrable.


Spache (Revised)

Similar to the Powers, Sumner, Kearl Write formula, the Spache test is also aimed at the younger set. It was published by George Spache in 1952, in The Elementary School Journal, and uses both a word list and sentence length to determine readability for children.

The actual formula is:

(0.121 x average sentence length) + (0.082 x percentage of unique unfamiliar words) + 0.659

The revised edition incorporates a different word list, and probably other tweaks, but like other readability tests it gives a final education-level grade that the writing would be suitable for.



A great “catch all” and one of the most widely-known readability tests, the Flesch-Kincaid (or F-K) readability test is another that offers a final reading grade level based on US education.

The original version, Flesch Reading Ease, was devised by Rudolph Flesch while he was working for the Associated Press, but the US Navy later adapted it into the Flesch-Kincaid score we use today.

AutoCrit provides results from both the original Flesch Reading Ease test (score out of 100) and the updated Flesch-Kincaid readability test (approximate grade level).

With the original Flesch Reading Ease test, the higher the score, the more accessible it is. Typically, it tends to go up to 100, but you can actually get phrases that go higher than that – such as “the cat sat on the mat” which I believe is around 116.

You can also convert the Flesch Reading Ease score a grade level using the following table:

 Score  School Level
 100 – 90  5th grade — Very easy to read.
 90 – 80  6th grade — Easy to read. Conversational English for consumers.
 80 – 70  7th grade — Fairly easy to read.
 70 – 60  8th & 9th grade — Plain English.
 60 – 50  10th to 12th grade — Fairly difficult to read.
 50 – 30  College level, difficult to read.
 30 – 10  College graduate, very difficult to read.
 10 – 0  Professional, extremely difficult to read.

The Flesch-Kincaid test is pretty much the most-used one today. If you have any experience in marketing, you’ve most likely met a BUNCH of people who are absolutely obsessed with it, trying to get their grade score as low as possible – like a badge of honor that their copy is easily read by just about anyone.


Linsear Write

Linsear Write was actually developed by the US Air Force. Like the SMOG formula, this one is highly specialized – designed to gauge the complexity of air force technical manuals. The source of the idea traces back to a 1966 style manual called Gobbledygook Has Gotta Go, which pointed out the importance of shorter words.

Even when something is highly technical and susceptible to an overload of jargon, it still needs to be accessible!

Here, “easy” words (with two or fewer syllables) are given 1 point. “Hard words” are given 3 points. Divide the points by the number of sentences in a 100-word sample, and then adjust the provisional result r:

If r > 20, Lw = r / 2.
If r ≤ 20, Lw = r / 2 – 1.

Your result is, as with other tests, a required US grade level for reading.


Why should you care about Readability Statistics?

Well, according to the folks at Readable.com, your book is accessible to 85% of the public if it has a readability grade of 8 or lower.

And if you improve your readability from a grade 12 level to a grade 5 level, you get an 83% increase in the number of people who will finish reading.

That’s a massive difference!


The bottom line

Readability statistics can be a useful but blunt tool. The resulting scores provided are only as relevant as the data and statistics used as input. Many of the tests are not applicable to the genre and audience and the resulting scores/grade levels can be misleading.

That being said, when used in the right context, these analytic tools are a quick and efficient way to determine how well your audience will comprehend your work.


Write better. Right now.