Readability is a crucial skill to have as a writer. Whether you’re a content marketer, educator, author, technical writer or healthcare professional, keeping your audience in mind is key. But, what is the history of readability, and what can it teach us?

English language history: some perspective

In 1595, in the Elizabethan era, the average sentence length was 41 words. Only one-third of England’s population was literate.

Jump forward to the 1820s and the average sentence length was almost halved to 26 words.

Literacy rose massively during the Victorian era and the consumption of popular fiction, such as penny dreadfuls, marked a new era of publishing.

By the 1950s, the rise of television had begun. The number of US homes with TV sets hit one million and by this time, the average sentence length was 14 words.

It’s clear that the evolution of the English language came with a continual shortening of the sentence. The expansion of different types of media has brought with it a double-edged sword.

That we have different ways of communicating than we have had in the past is a beautiful thing. That we know more about current events than ever is quite the phenomenon.

But, with this influx of information came a shortening of our attention spans. The efficiency of communication has become key in a world swimming with information.

When did readability first become popular?

Methods of calculating readability had been explored within the education sector exclusively, but it didn’t become a major marketing tool until the readability expert Rudolf Flesch got involved.

Flesch saw the potential not only of challenging approaches in education but also of advocating plain English for everybody.

He published the readability formula Flesch Reading Ease in 1948. The higher the score according to this calculation, the more readable the text. It can be interpreted using the table below.

Score School grade Notes
100.00-90.00 5th Very easy to read
90.0–80.0 6th Easy to read.
80.0–70.0 7th Fairly easy to read
70.0–60.0 8th and 9th Plain English. Easily understood by 80% of Americans
60.0–50.0 10th to 12th grade Fairly difficult to read
50.0–30.0 College Difficult to read
30.0–0.0 College graduate Very difficult to read


Flesch’s Reading Ease was the first popular readability test and has become ubiquitous and widely respected. So much so that it’s used fiscally.

In some cases, it has become a government-enforced requirement that insurance policies have a good Reading Ease score. The UK government also recommends the use of Readable to its staff.

It was of particular interest to the publishing and journalism sectors, who noticed a surge in readership when using Flesch formulas to improve their readability.

Robert Gunning, an American businessman who worked in the publishing sector, recognized this. He followed up with his own algorithm, the Gunning Fog Index in 1952.

Gunning created the formula after facing criticism about the readability of his own writing. He was trying to write a ‘scathing rebuttal’ and realized that although he was aggravated by the accusation, he found himself writing more simply.

Even just being aware of readability issues, he weighed his sentences more carefully in favor of pared-down prose which was friendlier to his readers.

His grading was in line with US education grades, similarly to how Flesch Reading Ease scores are converted.

What is the plain language movement?

The plain language movement is all about keeping the consumer’s interests in mind.

The movement for plain language originally came out of the consumer movement. This began in the US in the 1960s, focussing on consumers’ rights.

New technology and the explosion of television advertising meant there were many ethical questions about transparency, safety and social impact.

Man men storyboard | free readability test

The consumer movement gained momentum throughout the 1970s and secured more product regulation. As it was so concerned with clarity of messaging, plain language naturally became an important focus.

Plain language was also shown by an influx of new readability algorithms. Perhaps the most indicative of the era was the Automated Readability Index, designed for military use in the late 1960s.

This is because it acknowledged that new technology is an advantage to the accuracy of readability calculations. The common use of typewriters demanded a mechanical method of tabulation.

Rudolf Flesch was also at the forefront of developing formulas which would help in government and the military.

Drawing on his previous Reading Ease formula, he worked with the US Navy to develop the Flesch Kincaid reading grade level. Flesch Kincaid calculates the US school grade level of a text’s readability.

This was tested on the Navy’s technical material and after testing in the 70s became military standard. It also was connected to legal readability requirements in many states.

The plain language movement continues to make waves in readability issues worldwide.

In 2018, there was a campaign for UK doctors to use plain English when writing to patients. Studies showed many patients were making appointments just to have impenetrable jargon explained to them.

What’s next for readability?

Today, in the computer age, we have quicker and easier tools than ever for measuring readability.

ReadablePro uses a range of the most respected and reliable formulas to generate a letter grade of readability which is simple and easy to understand.

It also provides guidance on how to improve readability such as shortening sentences, using less difficult words and using a more active voice.

We’re proud to support associations such as Clarity and PLAIN who advocate plain language worldwide.

Clarity and readability of writing remain a crucial issue in marketing, law, healthcare and much more. It’s also become increasingly recognized as a valuable SEO tool, helping writers to create content their readers want to stick around for.

Whatever you’re writing, keep your audience in mind.

As the celebrated Wall Street Journal editor Bernard Kilgore once said:

“Write for the expert, but write so the non-expert can understand.”

Laura Kelly

Laura is a content writer and customer success champion at Readable. She's a Literature MA graduate who loves poetry, a good coffee and 35mm photography.