When writers first hear the phrase “grade level,” they assume it belongs to children’s books and YA. Picture books for kindergartners, middle grade for ten-year-olds, and then—once you’re writing for adults—the training wheels come off and you can write however you like.
Not quite. Every piece of prose has a measurable reading level, including literary fiction, thrillers, romance, and that sprawling epic fantasy in your drafts folder. And the reading level of your adult novel matters far more than most first-time authors realize.
Why It Matters
Grade level isn’t a measure of how smart your ideas are. It’s a measure of how much work a reader has to do to extract them. The formulas behind readability scores—the most famous being Flesch-Kincaid—look at mechanical things: how long your sentences run and how many syllables your words carry. Long, winding sentences full of polysyllabic vocabulary score high. Short, direct sentences with plain words score low.
Here’s the counterintuitive part: for fiction, low is usually good.
Reading fiction is a leisure activity. Your reader has had a long day, and they’re choosing your book over their phone, their TV, and sleep. Every extra ounce of effort your prose demands is friction, and friction is where readers put books down. This is why analyses of bestselling fiction consistently find that commercial hits cluster at surprisingly modest reading levels—not because the books are simple-minded, but because the prose stays out of the way of the story.
The famous case study here is Shane Snow’s readability analysis of bestselling authors. He found that Jane Austen wrote at just above a 5th grade level, Stephen King at about a 6th grade level, Tolkien slightly above 6th, and Tolstoy around 8th. The bestselling fiction he examined all landed between 4th and 9th grade readability. To Kill a Mockingbird—a Pulitzer winner taught in literature classes—scores around a 4.6 on the Flesch-Kincaid scale.
Simple prose is not simple thinking. Hemingway built a Nobel Prize on that distinction.
How It Has Changed Over Time
If you pick up popular novels from the 19th and early 20th centuries, you’ll notice the sentences breathe differently. Dickens, Hawthorne, and Melville wrote long, clause-stacked sentences for an audience that read fiction as a primary form of entertainment and expected—even savored—density. Classic novels routinely measure at 9th grade level and above.
The trend since then has been a steady march toward accessibility. One analysis of #1 bestsellers found the average sentence length dropped from about 17 words in the 1960s to about 12 words in the 2000s, and that 28 chart-topping bestsellers since the 1960s scored below a 5th grade reading level—26 of them published after 2000. Multiple readability formulas (Flesch-Kincaid, Dale-Chall) show the same downward drift.
Why? A few forces are at work. Fiction now competes with film, television, games, and infinite scrolling, so prose that moves fast holds an advantage. Journalism led the way—Rudolf Flesch originally developed his readability formula in the 1940s while consulting for the Associated Press to make newspapers easier to read. Genre fiction’s explosive growth rewarded pace over ornament. And the sheer size of the modern reading audience means books that only advanced readers can comfortably enjoy are fishing in a smaller pond.
None of this means literary complexity is dead. Plenty of acclaimed novels score higher, and some readers seek out exactly that. But if you’re writing commercial fiction and hoping for a broad audience, the current of the market flows toward clarity.
What Should You Target?
For most adult commercial fiction—thrillers, romance, mystery, contemporary, upmarket—aim for roughly grade 6 to 8 on the Flesch-Kincaid scale. Eighth grade is often cited as the average reading level of the general public, and most adults prefer recreational reading a couple of grades below their maximum ability. Grade 6–7 is the sweet spot where King, Rowling, and most of the bestseller list live.
A few nuances:
Literary fiction has more room to run higher, into the 8–10 range, because its audience self-selects for readers who enjoy denser prose. But even here, higher scores should be a deliberate stylistic choice, not an accident of overwritten sentences.
Genre conventions matter. A cozy mystery reader and a hard science fiction reader have different tolerances. Read comparable titles in your genre and check where they land.
And remember what the score doesn’t measure: theme, subtext, structure, emotional depth. You can explore grief, war, and moral collapse at a 5th grade reading level. The score only tells you how hard the sentences are, not how deep the book is.
How to Test Your Own Writing
The good news is that testing takes minutes.
Microsoft Word has readability statistics built in. Enable “Show readability statistics” in the proofing options, run a spelling and grammar check, and Word will report your Flesch Reading Ease and Flesch-Kincaid Grade Level.
Hemingway Editor (free in the browser) highlights hard-to-read sentences, adverbs, and passive voice, and displays a grade level in real time as you edit. It has no word count limit, so you can paste in entire chapters.
Readable and similar dedicated tools run your text through multiple formulas at once—Flesch-Kincaid, Gunning-Fog, SMOG, Dale-Chall—which is useful because each formula has quirks, and an average across several is more trustworthy than any single score.
A practical workflow: don’t check readability while drafting. Write the story. Then, during revision, run a few representative chapters through a checker. If you’re scoring above grade 8 and you’re writing commercial fiction, hunt for the usual suspects—sentences over 25 words doing three jobs at once, Latinate words where short ones would do (“utilize” for “use,” “commence” for “begin”), and stacked prepositional phrases. Break long sentences at their natural joints. Read the revision aloud; if you run out of breath, your reader ran out of patience.
One warning: don’t chase the number into the ground. A manuscript where every sentence is eight words long reads like a ransom note. Rhythm comes from variation—short sentences for impact, longer ones for flow. The grade level is a diagnostic, not a destination.
Your job is to make the reader forget they’re reading. A reasonable grade level is simply one of the tools that gets you there.
Further reading and tools:
- Flesch-Kincaid Readability Test and Calculator — Hemingway Editor
- Flesch Reading Ease and the Flesch-Kincaid Grade Level — Readable
- Readability is a Key Skill of the Best-Selling Author — Readable
- What Do Reading Level Tests Say About Bestselling Books? — Ebook Friendly
- What Writers Need to Know About Readability — Literature Lust
