Readability scores show up in a lot of writing tools, and most of them hand you the number with no context. A Flesch Reading Ease of sixty six, a Grade Level of nine point two. Fine. But what is that telling you about your prose?

The short answer is that both scores boil down to two things: how long your sentences are and how complicated your words are. That is all. The scores are not measuring style, voice, insight, or anything you would normally call good writing. But knowing what they measure makes them useful, and knowing what they do not measure keeps you from chasing the wrong number.

Flesch Reading Ease: the easy-to-read score

Flesch Reading Ease runs from zero to one hundred, where higher means easier. It is computed from the average number of words per sentence and the average number of syllables per word. Short sentences made of short words score high. Long sentences made of long words score low.

A rough map:

90 to 100: fifth grade. Very easy. Children’s books.
70 to 90: sixth to eighth grade. Most commercial fiction, most magazines.
60 to 70: ninth grade. Plain English. Most journalism and general nonfiction.
50 to 60: high school. Getting denser. Literary fiction, trade nonfiction.
30 to 50: college. Academic, specialist, or deliberately challenging.
Under 30: post-graduate. Most readers will struggle without a reason to care.

Flesch-Kincaid Grade Level: the same information, reshaped

Flesch-Kincaid Grade Level takes the same two inputs, sentence length and syllable density, and produces a US grade level. A score of eight means roughly an eighth grader should be able to read the passage. This scale tracks the Reading Ease score almost exactly, just inverted. Higher grade level means harder.

You rarely need both numbers. The grade level is easier to reason about if you are writing for a specific audience, and the reading ease is easier if you are tracking your trend over time.

What readability is not measuring

These scores do not see metaphor, irony, implication, or beauty. A paragraph of Hemingway might score high. A paragraph of Nabokov might score low. That does not mean one is better than the other. It means the scores are measuring accessibility, not quality.

They also do not measure whether your reader is interested. A sentence can be very easy to read and still be boring. Do not use these numbers as a proxy for good writing. Use them as a proxy for one specific question: is this as hard to read as I meant it to be?

A practice loop for readability

Decide who you are writing for. A beach reader, a specialist, a YA audience.
Pick the Flesch Reading Ease target that roughly matches. For most commercial fiction, 70 to 80. For a general essay, 60 to 70. For literary fiction, 50 to 65.
Paste a page into the Prose Grade tool and note the reading ease.
If it is far off from your target, look at the usual culprits. Long sentences with no break. Latinate vocabulary when an Anglo-Saxon word would do. Subordinate clauses that pile up.
Rewrite one paragraph. Re-grade. Watch the score move.

When to ignore the score

Sometimes your readability score should be low. A dense passage of interior monologue, a scene of grief, a piece of experimental fiction. The score is a tool for catching drift you did not mean to introduce, not a scold. If your low score is doing a job, leave it.

The point is to know. A writer who knows their reading ease is sitting at forty eight and chose it is in control. A writer whose reading ease has quietly drifted from seventy two to forty eight over six months without noticing is not.

When you want to watch your readability across every draft, sign up free. A six month trend will teach you more about your prose than any single score.