Categories: Readability

by Jonathan Gillham


Flesch Kincaid Reading Ease Formula

If you go back in time, to the 19th century in the USA, schools were quite different from what they are now. Students were never graded on their reading abilities until 1847. A school in Boston was opened where children were given books to read according to what grade they were in. The teachers wanted to teach the children in simple, plain English, rather than use highfalutin vocabulary.  They developed simple readability formulas that would be easy to read for their students.

The real breakthrough of readability formulas came when Edward Thorndike wrote a book, The Teacher’s Word Book in 1921. More works on this topic were followed by other authors, such as George Kingsley Zipf and Rudolf Flesch. Rudolf Flesch’s formula, the one we are talking about today, is called the  Flesch-Kincaid Grade Level. Today there are over 200 readability formulas and people are debating all the time which are the best, the real foolproof ones. They all try to improve the readability of text.

Basically, what is the Flesch Reading Ease Score in a nutshell?

Finding Out About The Flesch Kincaid Reading Ease Formula

The bottom line is The Flesch Reading Ease Test measures the readability of the text you are reading. To achieve and determine a reading score, the length of your sentences is measured, as well as the average number of syllables you use in each word. You will end up with a score somewhere between 0 and 100.  If you receive 100, it would mean that your copy is easy and simple for people to read and understand. Obviously, if the score was 0, your text would be hard for people to read and understand.

The specific mathematical formula looks like this:

RE, or readability ease = 206.835 – (1.015 x ASL, or average sentence length which is the number of words divided by the number of sentences) – (84.6 x ASW, or an average number of syllables per word which is the number of syllables divided by the number of words).

Look at what the scores mean:

Flesch Reading Ease Score

The results:

If you write a text that consists of short sentences and the words only have a couple of syllables in them, the text will end up with a very high Flesch reading ease score, i.e. easy to read. If the text has a very low Flesch reading ease score it will be difficult to read. That’s because the text consists mostly of very long sentences with difficult and complex words in them.

How did the Flesch reading ease score come about?

Flesch Reading Ease Formula is considered as one of the oldest and most accurate readability formulas. Rudolph Flesch, an author and readability expert, developed this formula in 1948. He wrote an article, A New Readability Yardstick, where he proposed the Flesch Reading Ease Readability Formula.

The importance of the Flesch Reading Ease Score for SEO and reading

Are you someone who is writing copy for websites? If you are using very complicated language, the people reading it might have trouble understanding what they read. They might leave that website and move on to another where they find easier information to read. A website that doesn’t get a lot of clicks on it because of this can lead to lower rankings. It’s important to write clearly and simply.

The readable text brings in the higher rankings

Still, it can be tricky to write readable text.

You can use the Flesch Reading Ease Score to improve your writing. If you are writing for an audience to read, your writing should be easy to read. That’s because you will reach a broad spectrum of people. You could write on complex topics if your audience was an academic audience for instance. But if you really want to benefit from the results that a Flesch Reading Ease Score gives you, then you need to focus on just two simple things:

  • Keep your sentences short: Long sentences make it difficult to read. Short sentences make it possible for the reader to absorb what they are reading. 
  • Try and limit using long and difficult words: Some words that contain more than four or so syllables are difficult to read. It is best to avoid using them. Use simpler words instead of long, more difficult words that have the same meaning. For example, use the word “use” instead of “utilize.” 

If you are writing for a large and broad audience, you should try and avoid the typical jargon that some of the experts in their field like to use. A medical doctor might use words like intravenous, or esophagus. But if the person isn’t a medical fundi, then they might battle reading those words, not understanding much in the article.


Remember when you talk of the Flesch Reading Ease Score Formula, it might sound like math. But language isn’t math. Readability depends on lots of other things besides the formula. The Flesch Reading Ease Formula is really a simple approach to assessing the grade levels of readers. It assesses the difficulty of a reading passage written in English. For instance, as we mentioned above, Rudolf Flesch developed these methods to improve the readability of newspapers.

Now, it’s many years later, and the Flesch Reading Ease is being used by marketers, writers, research communicators, and many others. Everyone uses it to help them assess and make easy the piece of text that is to be understood and engaged with.

Readability scores give a person insight into how easily they understand the text. A lot will depend on how easy and engaged they are with what is written. This means that if you have a readable website with engaging content, you can only boost your business or organization.

About the Author: 

Jonathan Gillham

Founder / CEO of Originality.AI

I have been involved in the SEO and Content Marketing world for over a decade. My career started with a portfolio of content sites, recently I sold 2 content marketing agencies and I am the Co-Founder of, the leading place to buy and sell content websites. Through these experiences I understand what web publishers need when it comes to verifying content is original. I am not For or Against AI content, I think it has a place in everyones content strategy. However, I believe you as the publisher should be the one making the decision on when to use AI content. Our Originality checking tool has been built with serious web publishers in mind!

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