Optimising Text Readability: Because Nobody Reads What They Don't Understand

Let's be real: people online don't read - they scan. And if your content isn't readable, they'll bounce faster than a rubber ball on concrete.

So let's talk readability. Specifically, how you can measure it, improve it, and use it to supercharge your website's performance. Plus, a bonus: how to track it in Google Tag Manager like a total pro.

What is Readability?

Readability is how easy it is for someone to read and understand your writing. Simple, right?

But here's the thing - not everyone reads at the same level. Literacy is a spectrum:

• At one end, you have people who struggle with basic comprehension. This is known as functional illiteracy - someone may technically be able to read, but not well enough to manage daily tasks like reading a bus timetable or understanding a prescription label.
• At the other end, you've got people writing scientific journals about quantum something-or-other.

Most people sit somewhere in the middle. So if your website copy sounds like Shakespeare met ChatGPT in a philosophy class, you're probably losing customers.

Why Readability Matters (Seriously)

According to the OECD, 15 - 20% of adults in developed countries are functionally illiterate. That means they can't easily read or understand complex text. If your website or marketing content is aimed at these users - but reads like a government policy paper - you're in trouble.

Good readability = faster understanding. Faster understanding = better engagement.

And here's the kicker: readability becomes even more important depending on the device your user is on. A paragraph that's fine on a desktop might look like a terrifying wall of text on a phone.

TL;DR:

• Keep it short.
• Keep it clear.
• Make it scannable.

The Automated Readability Index (ARI): Born in Battle

The Automated Readability Index was developed by the US Navy. Yes, that Navy.

They needed a way to make sure training manuals could be understood by sailors with varying levels of education. So they created a formula that scores text based on sentence length and word complexity. The result? A number that tells you the grade level someone would need to understand it.

Since they were using mechanical typewriters, ARI focused on stuff you could literally count: characters, words, sentences. That makes it a pretty great match for analysing digital content.

Here's the basic formula:

ARI = 4.71 × (characters/words) + 0.5 × (words/sentences) - 21.43

Here's one sentence rewritten three ways to show what we mean:

A score of 5 means a (US) 5th grader can understand it. A score of 12? You'd better hope your reader passed Year 12 English.

Tracking Readability in Google Tag Manager

If you're feeling a bit geeky and want to track readability dynamically on your site, you can do it with some custom JavaScript in GTM.

function() {

  // Change this CSS selector to match your content container          
  var selector = '.blog-content'; 
  var container = document.querySelector(selector);

  if (!container) {
    return null;
  }

  var text = container.innerText || container.textContent || '';
  var sentences = text.match(/[^\.!\?]+[\.!\?]+/g) || [];
  var words = text.trim().split(/\s+/);
  var characters = text.replace(/\s+/g, '').length;

  var sentenceCount = sentences.length || 1;
  var wordCount = words.length || 1;

  var ari = (4.71 * (characters / wordCount)) +
            (0.5 * (wordCount / sentenceCount)) - 21.43;

  return Math.max(1, Math.round(ari));
}

You can send this ARI score as a custom dimension against your pageview and other in-page events. That way, you can see whether users are engaging more with simpler vs. more complex content.

Analysing Readability's Impact on Engagement

Here's where it gets juicy. When you track readability you can start to ask questions like:

• Does lower ARI = higher time on page?
• Do people scroll deeper when things are easier to read?
• Is there a sweet spot where readability drives conversions?

In many cases, yes - simpler = better. People want to scan, understand, and move on.

Example: Maybe your FAQ page with an ARI of 5 keeps users around for 3 minutes. But that blog post with an ARI of 11? They're bailing after 20 seconds.

Over time, this helps you figure out whether simplifying your content actually increases conversions. Spoiler alert: it usually does.

But Wait - Sometimes Complex is Okay

There are exceptions. If your audience is technical - say, software engineers reading API documentation - they might actually need complexity. A dumbed-down version of your technical page could make them lose trust.

Example:
If you're selling crypto auditing services to fintech CTOs, a bit of jargon might be a good thing.
If you're selling socks? Keep it light, fun, and readable by a 12-year-old.

Final Word

Don't assume people will work hard to understand your site. They won't. If you want people to do something - buy, subscribe, book an appointment - you need to make it ridiculously easy for them to understand what you're saying.

And that starts with readability.