Why do some pieces of writing feel effortless to read while others feel like wading through mud? The answer lies in a field of study that has been around for nearly a century: readability science. At its core, readability is about how easily a reader can understand written text. And the evidence is clear: short words and short sentences nearly always win.
What Is Readability?
Readability is a measure of how easy a text is to read and understand. It is influenced by factors such as word length, sentence length, syllable count, and the complexity of sentence structure. While readability does not capture everything that makes writing good (such as tone, argument quality, or emotional impact), it is an excellent predictor of whether your audience will actually finish what you wrote.
Researchers have developed dozens of formulas to measure readability, but one stands above the rest in both longevity and popularity: the Flesch Reading Ease formula.
The Flesch Reading Ease Formula
In the 1940s, Austrian-born American author Rudolf Flesch set out to answer a practical question: what makes some writing easier to read than others? He studied thousands of text samples and identified two variables that correlated most strongly with reading difficulty: average sentence length and average syllables per word.
The Flesch Reading Ease formula calculates a score between 0 and 100, where higher scores indicate easier readability. The formula is:
Score = 206.835 – (1.015 × ASL) – (84.6 × ASW)
Where ASL is the average sentence length in words, and ASW is the average number of syllables per word.
A score of 60–70 is considered standard English, comparable to the readability of Time or Reader’s Digest. A score above 80 is considered “easy,” while a score below 30 is “very difficult” and typical of academic journals or legal documents.
Readability Score Reference Table
| Flesch Score | Difficulty Level | Typical Publication | Average Sentence Length | Syllables per Word |
|---|---|---|---|---|
| 90–100 | Very Easy | Children’s books | 8–10 words | 1.2 |
| 80–89 | Easy | Comics, popular magazines | 12–14 words | 1.4 |
| 70–79 | Fairly Easy | Consumer marketing | 14–16 words | 1.5 |
| 60–69 | Standard | Time, Reader’s Digest | 16–20 words | 1.6 |
| 50–59 | Fairly Difficult | The New York Times | 20–24 words | 1.7 |
| 30–49 | Difficult | Academic journals | 24–28 words | 1.8 |
| 0–29 | Very Confusing | Legal documents, insurance policies | 28+ words | 2.0+ |
Why Short Words Win
Short words have Anglo-Saxon origins. Words like “help,” “food,” “home,” and “love” come from Old English and have been part of the language for over a thousand years. Longer words often come from Latin, Greek, or French and entered English through academic and legal channels.
The result is that short words feel more familiar. They require less cognitive effort to decode. When a reader encounters the word “utilise,” the brain must work slightly harder than when encountering “use.” Multiply that difference across an entire document, and the cumulative effect on reading speed and comprehension is substantial.
The Case Against Jargon
Jargon is not always bad. Within a specialised community, precise technical language allows experts to communicate efficiently. The problem arises when writers use jargon not because it is necessary but because it sounds impressive. If you can replace a jargon term with a plain-English equivalent without losing meaning, do it.
Before: We need to facilitate the utilisation of core competencies across verticals.
After: We need to use our strengths across departments.
Why Short Sentences Win
The optimal sentence length for comprehension is 15 to 20 words. Sentences longer than 30 words cause a sharp drop in reader comprehension, even for skilled readers. The reason has to do with working memory: readers must hold the beginning of a sentence in mind while processing the middle and end. The longer the sentence, the more cognitive load it imposes.
Consider this 45-word sentence:
Due to the fact that the quarterly revenue projections were revised downward following the unexpected decline in consumer spending during the third quarter, management has decided to postpone the planned expansion of the European operations until the start of the next fiscal year.
Now see the same information broken into shorter sentences:
Quarterly revenue projections were revised downward. Consumer spending declined unexpectedly in the third quarter. As a result, management has postponed the European expansion until the next fiscal year.
The second version is 60% shorter and much easier to understand on a single reading.
The History: Rudolf Flesch and the Readability Movement
Rudolf Flesch was born in Vienna in 1911 and fled Austria in 1938, just before the Nazi annexation. He settled in the United States, where he earned a PhD in library science from Columbia University. His 1949 book, The Art of Readable Writing, became a bestseller and changed how American businesses and government agencies approached writing.
Flesch argued that clear writing is a civic virtue. He believed that government documents, insurance policies, and legal contracts should be understandable to the average citizen. His work directly influenced the Plain Language Movement, which later led to the Plain Writing Act of 2010 in the United States.
Applying Readability Science to Your Writing
You do not need to calculate Flesch scores manually. Many tools (including CopyRefine’s Readability Score tool) do it for you. Here are the practical takeaways:
- Aim for 15–20 words per sentence. Vary your sentence length to avoid monotony, but keep the average in this range.
- Prefer short, familiar words. Use “use” instead of “utilise,” “help” instead of “facilitate,” and “try” instead of “endeavour.”
- Keep paragraphs short. Three to five sentences per paragraph is ideal for online reading.
- Write for a Flesch score of 60 or higher. That is “standard” or “fairly easy” readability, which suits most general audiences.
- Test your writing with a readability tool. Know your score and adjust accordingly.
Readability science has been around for over 80 years, yet most writers still ignore it. That is good news for you: by applying these simple principles, your writing will stand out as clearer, more accessible, and more effective than the competition.