Readability Checker: The Complete Guide (2026)

What readability scores measure

Every common readability formula rests on two observations that have held up for almost a century: long sentences are harder to follow than short ones, and long words are harder than short ones. The formulas differ only in how they weight those two factors and what they output. Feed them the same text and they all read the same raw ingredients, the count of words, sentences, and syllables, then turn those into either a difficulty score or a school grade.

That simplicity is the strength and the limit. The scores are objective, fast, and repeatable, which makes them useful for editing and for meeting plain-language rules. But they cannot judge whether a sentence is clear, whether an argument flows, or whether a word is the right word. A passage of short sentences full of jargon can score easy and still confuse. Treat the number as a smoke detector, not a substitute for reading the work.

Flesch Reading Ease

Flesch Reading Ease returns a number from 0 to 100, and unlike the others, higher means easier. The formula subtracts penalties for long sentences and long words from a base of about 207. A score in the 60 to 70 band is plain English that most adults read without effort. Above 80 is very easy and conversational. Below 30 is the dense register of academic papers and legal contracts. It is the score to watch when your goal is broad reach.

Flesch-Kincaid Grade Level

Flesch-Kincaid takes the same inputs and reports a US school grade instead of a 0 to 100 scale. A result of 8 means an average eighth grader can read the text. It is the most widely cited readability number, built into word processors and required by many style guides. For general web writing, grade 7 to 9 is the sweet spot. The grade level is intuitive precisely because everyone has an instinct for what an eighth-grade reading level feels like.

Gunning Fog

The Gunning Fog index estimates the years of formal education a reader needs, and it adds a factor the Flesch formulas leave out: the proportion of complex words, defined as words of three or more syllables. That makes Fog sensitive to jargon in a way reading ease is not. A Fog index of 8 is easy, 12 is the practical ceiling for a general audience, and above 17 is graduate level. If your reading ease looks fine but the Fog index is high, the culprit is usually a few long technical terms doing a lot of damage.

SMOG

SMOG, the Simple Measure of Gobbledygook, also counts complex words and outputs a grade, but it was tuned to predict near-complete comprehension rather than the average. That is why it is the formula of choice in healthcare, safety, and consent documents, where a reader has to understand almost everything, not just the gist. SMOG is most reliable on passages of thirty sentences or more. On a short paragraph it still gives a useful signal, but treat it as approximate until the sample is long enough.

What score should you aim for

There is no universal target, only a target for your audience. General web and marketing content aims for Flesch Reading Ease of 60 to 70 and grade 7 to 9. News writing sits around grade 8. Government and healthcare plain-language guidance usually wants grade 8 or lower, sometimes grade 6. Academic and professional writing accepts grade 13 and up because the readers are specialists who expect the density. The mistake is treating a low grade as always better. Writing for experts at grade 6 can feel patronizing and waste their time; writing for a general audience at grade 14 loses them. Match the score to the reader.

How to lower the grade level

When a draft reads two or three grades too high, the fixes are mechanical and reliable. Split long sentences. The single biggest lever is average sentence length. A 40-word sentence that becomes two 20-word sentences drops the grade immediately, with no loss of meaning. Swap long words for short ones where a short one exists. "Utilize" becomes "use," "facilitate" becomes "help," "in order to" becomes "to." Cut the throat-clearing. Phrases like "it is important to note that" add syllables and sentence length without adding meaning. Prefer the active voice, which is usually shorter and more direct than the passive. Run the draft through the checker, make one pass of these edits, and watch the grade fall. A word counter helps you keep an eye on length while you trim.

Readability and SEO

Google does not rank pages by Flesch score. There is no readability ranking factor. But readability and ranking are connected through behavior. Text that is easy to read holds attention, earns longer visits, and gets shared and linked more often, and those behaviors do influence ranking. The practical takeaway is the same as the writing advice: for content meant to reach a wide audience, write at grade 7 to 9. That is not a call to oversimplify. It is a call to write clearly, with sentences a reader can hold in their head and words they do not have to decode. Clear writing wins readers, and readers are what search engines are ultimately measuring.

The limits of readability formulas

The formulas were built for running prose, so they mislead on anything else. A page of bullet points, headings without periods, code blocks, or tables confuses the sentence count and produces a score that does not reflect how the page actually reads. They also cannot detect whether short, simple sentences are actually clear; a string of jargon-filled short sentences scores easy and reads hard. And the syllable estimate, while accurate enough across a paragraph, occasionally miscounts an unusual word. Use the scores to find passages worth a second look, then trust your own reading for the final call.