How do readability scores apply to email content?

You've probably seen a readability score before: a Flesch-Kincaid grade level, a Gunning Fog index, a Hemingway app highlight. For long-form content, they're a useful gut check. For email, they still apply, but with constraints that make the numbers less important than the underlying principles they're measuring.

Readability formulas calculate a score by combining average syllables per word with average words per sentence. The Flesch-Kincaid grade level maps this to US school grade levels. A score between 6 and 9 means most adults can read it comfortably without effort. A score of 12 or higher means you're writing at academic-paper density. These formulas weren't designed for email (they predate it), but the principles they encode, shorter sentences, simpler words, consistent structure, translate directly to the medium.

Email adds variables that readability tools don't capture. Most of your subscribers are on mobile, where line lengths are shorter, rendering varies across clients, and attention spans are compressed further than on desktop. A paragraph that reads smoothly in a Hemingway Editor preview can feel like a wall of text on a phone because it wraps awkwardly. Mobile rendering is a readability variable that no formula captures. You have to test it visually.

And for For most marketing emails, target a Flesch-Kincaid grade level between 6 and 9. That's not about writing for a sixth grader. It's about respecting that your reader is distracted and skimming, not giving your copy their full attention. When your score comes back above 10, look for sentences you can split and words you can simplify. Cognitive load and readability are measuring the same thing from different angles: how much mental effort your copy demands.

The fastest workflow: paste your email copy into a readability checker after you draft it but before you design it. Flag sentences over 20 words, paragraphs over four lines, and words with four or more syllables where a simpler alternative exists. Then read it aloud. If you stumble, rewrite that sentence. That's the whole process.