If no one is reading your blog posts, you’ve got company. An Ahrefs study of about 14 billion pages found that 96.55% of pages get no traffic from Google. Readability is one of the reasons people leave a page. If it’s hard to read, they find something easier.
Average eyes glaze over when they see long sentences, difficult words, and walls of text. It’s painful. Most of us don’t like pain. So we avoid it. In this case, we bounce.
Simple, precise, readable documents tend to hold attention, reach more readers, and lead to sharing and conversions. That’s what you want, right?
A readability score is a way to measure the ease of reading a piece of writing. Here, we’re focusing on marketing content like blogs and websites. Readability scales also work for presentations, speeches, and even novels. Hemingway’s prose typically rates at a grammar school level, and he did well enough with it.
Adjust your work to lower your score and you’ll keep readers on the page longer. Google has not said it ranks pages by a readability score, and analysts have long debated how much it reads vocabulary, but pages people finish are more likely to earn shares, links, and return visits.
Reading scales such as SMOG, Gunning Fog, and the best known of them, Flesch–Kincaid, do some math that gives you a clear idea of how readable your text is.
Adjust, simplify, shorten, and you’ll usually get people to read on.
Takeaways
- Readability scores estimate the US school grade needed to read your text, using sentence length and word length or difficulty.
- Aim for about grade 6 to 8 for blogs and websites. Use Flesch–Kincaid as your default, and try a second formula to check it.
- Technical subject matter does not excuse hard-to-read sentences. Even a scientific manuscript can often come in around grade 8 or 9 with editing.
- Formulas count words and syllables, so they cannot judge accuracy or tone. Treat a score as a prompt to edit, not a verdict.
- Shorter sentences and familiar words help readers scan, absorb, and move on to more of your content.
Here’s an intro to readability and the most common readability tool formulas before you sit down and write an eloquent blog that no one reads.
What is “Readability”?
“Readability” is the property of being comparatively easy to read.
When you were in elementary school, you read “simple” books like Charlotte’s Web or Beverly Cleary’s Ramona books. These books have short sentences, easy narratives, and basic vocabulary. Kids love them, as do many adults. Ditto the Harry Potter series.
The ideas and lessons may not be “simple,” but the language is. That suits kids, and it suits adults too.
Later in high school, maybe you ran into 1984, with richer vocabulary, longer sentences, more words.
Or maybe you read The Catcher in the Rye, which is comparatively easy. Salinger’s prose is more readable than Orwell’s.
These are novels, though. Novels thrive on the author’s style and the art of words.
SEO blog posts typically don’t need to. White papers shouldn’t. Yet they often seem like dull novellas – big words, writers trying to “sound smart.”
Busy people don’t have the time or attention for Orwellian content. They want to scan and absorb, and with luck they’ll go on to read more of yours. Readability decides whether they do.
The Most Popular Readability Metrics
You can use any of these as a guideline to make your writing more readable. We prefer the Flesch–Kincaid grade, but it’s fun to try different ones. Here’s how they work.
This simple site lets you drop in your text and calculate them. Tools like Yoast SEO include a readability check as well. In our experience, their advice is often too blunt to act on.
Flesch Reading Ease Score
Rudolph Flesch’s formula starts from a set number and subtracts based on complexity and syllable counts. The result usually falls between 1 (very hard to read) and 100 (very easy to read), though very short or very complex passages can fall outside that range. The formula reads:
Flesch Reading Ease Score = 206.835 − (1.015 x average sentence length) − (84.6 x average syllables per word)
Scores for the Harry Potter books are commonly cited in the 70s and 80s, Moby Dick in the 50s, and legal and academic journals in the 30s or lower. For web copy, 70–80 is a good range. It reads easily without intense attention and still leaves room for maturity.
Flesch–Kincaid Grade Level
There’s a lot of Flesch in the game. And that last sentence is just the type of self-indulgent folly you should eliminate in your blogs.
Here we have the same Flesch, plus J. Peter Kincaid, who led a team that adapted Flesch’s work into a grade-level formula for the US Navy in 1975. It is the simplest grade-based tool to use, and it is the readability score Microsoft Word shows. If you’re looking for a standard, this is it.
We swear by it. (Sometimes we swear about it after we spend 2 days writing something, only to find it’s Grade 11.)
This formula calculates average words per sentence and syllables per word to create a grade level. Grades indicate the U.S. student grades. So, a grade of 8 means an 8th-grade student should be able to read and understand it reasonably well.
Reading Grade Level = (.39 × average sentence length) + (11.8 × average syllables per word) − 15.59
A good target for websites and blog articles is around grade 6. That doesn’t mean you’re expecting a bunch of 12-year-old readers. What it means is that people can read it easily. They can scan through it, get the relevant information, and consume more.
A common excuse is that more technical or scientific text, by its nature will be less readable. While technical terms must be precise, and chemical compounds can be long, subject matter is no excuse for lack of readability.
Even a scientific manuscript can be written and edited to achieve around a grade 8 or 9. Unless the peer reviewers insist that passive tense and big, unnecessary words are “more academic.” (They’re wrong!)
SMOG Index
An acronym for “simple measure of gobbledygook,” the SMOG Index is also based on an approximate grade level as a metric.
G. Harry McLaughlin introduced the SMOG Index in 1969 as part of his research on readability and clarity.
To use the index, a person should take 10 sentences in a row from the beginning, middle, and end of the text. That’s 30 sentences in total.
Next, count every word in the sentence list that has three or more syllables, including duplicates.
Take the square root of this figure and round it to the nearest whole number, and add three to this number to find the SMOG Index score.
More simply, the formula can be expressed as:
SMOG Index = 3 + (square root of polysyllabic count)
The SMOG Index number corresponds to grade levels up to 18, indicating college- and graduate-level reading levels.
SMOG Index
|
SMOG Score |
Reading Grade Level |
|
1–6 |
5 |
|
7–12 |
6 |
| 13–20 |
7 |
| 21–30 |
8 |
|
31–42 |
9 |
|
43–56 |
10 |
| 57–72 |
11 |
| 73–90 |
12 |
|
91–110 |
13 |
| 111–132 |
14 |
| 133–156 |
15 |
|
157–182 |
16 |
|
183–210 |
17 |
| 211–240 |
18 |
As with other readability scores, web content should aim for a grade of around 6–7, and 8 at the most. That balances maturity with ease of reading.
Gunning Fog Index
Attributed to American textbook publisher Robert Gunning, the Gunning Fog Index refers to his famous criticism of newspapers that Gunning believed were full of useless, “foggy” complex terms.
Gunning would go on to found the United States’ first readability firm in 1944. He spent his career working with dozens of newspaper writers and editors to streamline their publications.
The Gunning Fog Index takes a passage of at least 100 words and measures the ratio of words to sentences to derive average sentence length (ASL).
Next, count the number of three-syllable words (not including proper nouns or hyphenated words) and divide this number by the total word count to get a percentage of hard words (PHW). The Gunning Fog Index formula is then calculated by adding these two figures together and multiplying by 0.4.
Gunning Fog Index = 0.4 (ASL + PHW)
Although the Gunning Fog Index does not take into account that not all long words are inherently complex (e.g., “television”), it is relied on as a capable readability tool for SEO.
A Gunning Fog Index score of about 12 is usually considered too difficult for most people to read; commonly cited figures put leading newspapers like The Wall Street Journal at about 10 or 11 and TV Guide at around 6.
Websites should aim for about 6–8.
Coleman–Liau Index
Rather than using the sentence length or syllable length of some other readability tools, the Coleman–Liau Index measures reading level by the complexity of characters. Linguists Meri Coleman and T. L. Liau believed that the character count of letters in words was a better indicator of complexity than syllable count.
Coleman–Liau Index = 5.89 × (characters/words) – 0.3 × (sentences/words) – 15.8
As with Flesch–Kincaid, the Coleman–Liau score is a grade level. A 9.5 would suit a high school freshman.
As with the others, we aim for around a junior high level. Highly technical text may run higher, but that is often an excuse.
Automated Readability Index
The Automated Readability Index also combines characters per word and words per sentence. It was designed for computers and word processors to calculate quickly.
Automated Readability Index = 4.71 (characters/words) + 0.5 (words/sentences) − 21.43
Like Coleman–Liau, it returns a number that corresponds to a grade level, so the same 6–8 target applies to web content.
Dale–Chall Readability Formula
One of the oldest readability grade measurements, the Dale-Chall Readability Formula dates back to 1948, when it was published by linguists Edgar Dale and Jeanne Chall.
Dale, an Ohio State education professor, and Chall, the founder of the Harvard Reading Laboratory, took their inspiration from the Flesch scale, developing their formula for children above the 4th grade.
Unlike other metrics that look at word length, Dale–Chall looks at “hard” words, meaning words a 4th grader would not be expected to know. The original list had about 700 familiar words, and later editions expanded it to about 3,000. Words not on the list count as difficult.
These hard words are added up with a metric of average sentence length; this particular readability grade is valuable because familiar words are easier to read and understand than unfamiliar words, regardless of word length.
Dale–Chall Readability Formula = 0.1579 (percent difficult words) + 0.0496 (average sentence length)
If the percentage of difficult words is above 5% of the total, the formula includes an adjusted score:
Adjusted Dale–Chall Readability Formula = original score + 3.6365
Finally, Dale–Chall uses a table to gauge the reading level based on score:
Dale–Chall Readability Formula
|
Adjusted score |
Grade level |
| 4.9 and below |
4 and below |
|
5.0–5.9 |
5–6 |
|
6.0–6.9 |
7–8 |
|
7.0–7.9 |
9–10 |
|
8.0–8.9 |
11–12 |
| 9.0–9.9 |
13–15 (college/university) |
|
10 and above |
16 and above (college graduate) |
Conclusion on readability formulas
The average American adult is commonly said to read at about a 7th- to 8th-grade level. That does not mean they lack education, only that this is the level they read easily. Readers elsewhere are not much different.
So write like a normal person, and ask yourself whether you need those big words. Make your writing a pleasure to read.
Use readability tools on your site content, emails, and other text. You’ll likely see readers move on to more of your content, and some may make a purchase.
If you need help simplifying your language, we can chop and reword so your readers keep reading. See some examples. Ask us how we can help.
