Rudolf Flesch published his reading-ease formula in 1948, built from just two measurements: how many words a sentence runs, and how many syllables a word carries. It has no idea what the words mean, no sense of whether an argument holds together — and it is still, eighty years later, the fastest way to catch writing that is harder to read than it needs to be.

The two formulas

Flesch Reading Ease  = 206.835 − 1.015 × (words / sentences) − 84.6 × (syllables / words)
Flesch-Kincaid Grade =   0.39  × (words / sentences) + 11.8  × (syllables / words) − 15.59

Reading Ease runs roughly 0–100, higher is easier. Grade Level translates the same two inputs into a US school grade — a score of 8 means an eighth-grader could follow it. Both come from the same two numbers because both are proxies for the same thing: a sentence that keeps going, built from words that keep going, asks more of working memory than one that doesn’t.

Reading the score

• 90–100, Very easy — an average 11-year-old follows it without effort.
• 60–70, Standard — plain English, the band most general-audience writing aims for.
• 30–50, Difficult — best understood by college graduates; expected for a technical spec, a mistake for a landing page.
• Below 30, Very difficult — dense, academic, or legal writing.

There is no universal right answer — a legal disclosure and a recipe are not competing for the same score. The formula is useful for a different question: does this text land in the range its actual audience reads comfortably in, or did it drift somewhere else without anyone deciding that on purpose?

What the formula can’t see

A short, simple sentence that says nothing scores well. A long sentence that is genuinely clear — because its structure is doing real work, not because it’s padded — scores worse than it reads. The formula measures a proxy, not comprehension itself; it is a smoke detector, not a judge of the fire. Worth combining with an actual read-through, not a replacement for one.

Where a low score actually costs you

• Landing pages and pricing copy. A visitor deciding whether to sign up reads fast and skims; a sentence that needs a second pass is a sentence that gets abandoned instead of finished.
• The first two sentences of a section that answers a specific question — this is also the text a language model is most likely to lift verbatim into a direct-answer response, where plain, complete sentences quote more cleanly than a sentence built to be diagrammed.
• Instructions and how-to content, where a reader is trying to follow along in real time, not admire the prose.

Frequently asked

What score should a blog post aim for?

60–70 (Standard) covers most general-audience writing comfortably. Technical documentation for a specialist audience can sit lower without it being a problem — the question is whether the score matches who is actually reading it.

Why did my score change when I only fixed a typo?

The formula only reads word length, sentence length, and syllable count — a typo fix that changed word count even slightly shifts the ratio the whole score is built from. Small swings between edits are normal and not meaningful on their own.

Is Flesch-Kincaid the same as reading level?

It approximates US school grade level from the same two measurements, but it’s an estimate of sentence and word complexity, not a validated measure of comprehension for any specific reader.

Does this tool send my text anywhere?

No — pasted text is scored entirely in your browser. Fetching a URL makes one request to that page (to read its text), and the score itself is still computed locally.