Most people write and hit publish without giving a second thought to whether their readers can actually follow along. Not because they're lazy — they just assume that if they understand it, everyone will. That assumption quietly kills a lot of good content.
Readability scores exist to fix this gap. They turn the fuzzy question "is this easy to read?" into a concrete number you can act on. The two most widely used formulas — Flesch Reading Ease and Flesch-Kincaid Grade Level — were developed decades ago for the U.S. Navy to make technical documents less confusing for recruits. Today, word processors, content platforms, and newsrooms use them every day.
What the Flesch Reading Ease Score Actually Measures
The Flesch Reading Ease formula produces a score between 0 and 100 (though it can technically exceed those bounds). Higher means easier. The formula takes two inputs: the average number of words per sentence, and the average number of syllables per word.
Here's the formula: 206.835 minus 1.015 times the average sentence length, minus 84.6 times the average syllables per word.
Notice that syllables carry more weight (84.6 multiplier) than sentence length (1.015 multiplier). That's deliberate. Long words with many syllables — "comprehension," "implementation," "institutional" — are harder to process than long-but-simple sentences made of short words. "The dog ran into the house and barked at the cat sitting near the door" is a long sentence, but it's trivially easy to read because every word is one or two syllables.
Score ranges on the Flesch scale map to reading difficulty like this:
- 90–100: Very easy. Children's books, comic strips. Think "See Spot run."
- 70–90: Easy to fairly easy. Most popular novels, consumer emails, product descriptions.
- 60–70: Plain English territory. Most newspapers target this zone deliberately.
- 50–60: Fairly difficult. High school–level material, longer magazine features.
- 30–50: Difficult. Academic papers, technical manuals, white papers.
- 0–30: Very difficult. Legal contracts, medical research, some government documents.
The Flesch-Kincaid Grade Level and Why It's Different
The Flesch-Kincaid Grade Level (FKGL) uses the exact same two inputs but rearranges the math to output a U.S. school grade equivalent instead of a 0–100 scale. The formula: 0.39 times average sentence length, plus 11.8 times average syllables per word, minus 15.59.
A score of 8.0 means an average American 8th grader should be able to read the text without difficulty. A score of 12.0 maps to 12th grade. Scores above 16 suggest post-graduate reading level.
The key thing most people get wrong: a lower grade level is almost always better for general writing. The plain English movement has pushed professional writers toward grade 6–8 as a target for anything meant to inform a wide audience. The New York Times writes at around grade 10–11. BuzzFeed aims for grade 6. Neither is wrong — they're just targeting different readers.
Why Two Formulas and Not Just One?
They're actually measuring the same thing from two different angles, which makes them useful together. The Reading Ease score tells you how hard the reading experience feels. The Grade Level score tells you what educational background a reader needs to comfortably process the text.
A text can have a Reading Ease of 55 (fairly difficult) and a Grade Level of 10.5 — those two numbers are consistent with each other and both useful. Reading Ease is better for a quick gut check ("is this too dense?"). Grade Level is better when you're targeting a specific demographic ("I'm writing for college freshmen, so grade 13 is fine but grade 18 is not").
What Actually Moves the Needle
Run a paragraph through the checker, get a score of 38, and want to improve it? There are two levers:
Shorten your sentences. Every period you add pulls the average sentence length down. "The implementation of the new policy will require significant coordination between departments and stakeholders" is one sentence. Break it: "The new policy requires careful coordination. Departments and stakeholders must work together." Same information, better score.
Replace long words with shorter ones. This is where most of the gain hides. "Utilize" → "use." "Approximately" → "about." "Demonstrate" → "show." "Facilitate" → "help." "Subsequent" → "next." None of these swaps lose meaning. They cut syllables, which cuts ASW (average syllables per word), which dramatically raises your Flesch score.
You don't need to eliminate every long word. Technical writing legitimately uses technical terms — "photosynthesis" in a science article earns its syllables. The question is whether your long words are doing real work or just making you sound more formal.
Common Misreadings of the Score
A low Flesch score doesn't automatically mean your writing is bad — it means it's complex. If you're writing a pharmaceutical insert or a software API reference, grade 14 might be exactly appropriate. The score is only useful relative to your audience.
The opposite error is chasing a high score by writing in choppy fragments. "Dogs run. Cats meow. Birds fly." scores very high but communicates almost nothing. The goal isn't the number — it's matching the number to who's reading.
Also worth knowing: both formulas struggle with certain content. Very short texts (a single sentence) produce unreliable scores because the averages aren't stable. Texts with lots of numbers, abbreviations, or names can throw off syllable counts. And neither formula measures clarity, logic, or whether the content is actually accurate. A sentence can score perfectly and still be nonsense.
The Right Targets for Common Writing Types
Blog posts aimed at general readers: shoot for a Flesch score above 60, grade level around 8–10. Email newsletters: 65–75 is a sweet spot — easy enough to skim, serious enough to seem credible. Academic writing: grade 12–16 is normal and expected. B2B marketing copy often overshoots at grade 14+ when their audience would actually respond better to grade 10.
Landing pages and product descriptions benefit enormously from scores above 70. Conversion rate optimization studies consistently show that simpler copy outperforms "professional-sounding" dense copy — not because readers are dumb, but because people read online in a scanning, partial-attention mode. Easy text gets processed even when concentration is low. Hard text gets abandoned.
Running your writing through a readability checker should feel like a spell-check for complexity rather than a judgment on your intelligence. Writers who regularly check scores tend to develop an intuition for when they've accidentally drifted into academic mode — and they learn to pull themselves back before publishing.