Readability Checker: Flesch Reading Ease and Grade Level

By Alex Johnson. After building the syllable counter, the obvious next step was the score that syllables feed into. A single number is only half useful, though, so this checker also shows which sentences and words are pulling your score down.

Readability formulas boil a text down to two measurements: how long its sentences are and how long its words are. Long sentences make a reader hold more in mind at once, and long words tend to be less familiar. Neither measure knows what your text says, but together they predict reading difficulty well enough that they have been used for decades by schools, publishers, the US military and state insurance regulators.

What the scores mean

Flesch Reading Ease runs from 0 to 100, and higher is easier. Very short, simple text can calculate above 100 and very dense text below 0; the checker caps the displayed score at those ends. Most tools interpret the score with this scale, adapted from Rudolf Flesch’s own:

The Flesch-Kincaid grade level expresses the same two measurements as a US school grade. A grade of 8.0 means an eighth-grade reader should be able to follow the text. Because it is open-ended, it can go above 12 for academic writing.

The formulas

Rudolf Flesch published the Reading Ease formula in 1948 in the Journal of Applied Psychology, in a paper titled “A New Readability Yardstick”:

206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words)

In 1975, J. Peter Kincaid and colleagues recalculated it for the US Navy as a grade level, using reading tests taken by 531 enlisted personnel at Navy technical training schools in Memphis and Great Lakes (Research Branch Report 8-75):

0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59

The syllables term carries most of the weight in Reading Ease. Raising the average from 1.4 to 1.5 syllables per word costs about 8.5 points, about the same as adding eight words to the average sentence.

Why readability checkers disagree

Every tool uses the same formulas, so differences come from counting. Where does a sentence end after “Dr.” or “e.g.”? Is a heading a sentence? How many syllables are in “every” or “fire”? This checker skips common abbreviations and initials, treats each line without end punctuation as its own sentence, and counts syllables with rules that agree with the CMU Pronouncing Dictionary on 98.9% of the 5,000 most common English words.

To see how much syllable estimates move the score, I scored five passages twice: once with the checker’s rules and once with syllable counts looked up word by word in the CMU dictionary, keeping the word and sentence counts the same. “Rules” is the checker’s score and “Dict.” the dictionary-based one; the first two passages are the openings of each work.

The table shows raw scores, before the checker caps them at 0 and 100. Three of the five matched exactly. The largest gap, about 5 points, came from a technical paragraph full of rare words, which is where any rule-based count is weakest. Treat a score as a range of a few points rather than an exact figure.

How to make text easier to read

• Split the longest sentences first. Sort the sentence list by length and look for an “and,” “which” or “because” where one sentence can become two.
• Replace long words that have short equivalents. “Use” for “utilize,” “help” for “facilitate,” “about” for “approximately.” The long-words list shows which ones you repeat most.
• Keep the technical terms your reader needs. A medical or legal term the reader must know is worth its syllables; cutting it to raise a score makes the text less clear, not more.
• Vary sentence length. A text where every sentence runs 12 words scores well but reads flat. An average under 20 words leaves room for both short and long sentences.

Where readability scores are required

Some laws set a minimum score. Florida, for example, requires most insurance policies sold in the state to reach at least 45 on the Flesch Reading Ease test (Florida Statutes section 627.4145). The statute spells out its own counting rules: a contraction or hyphenated word counts as one word, a period, semicolon or colon ends a sentence, and headings, captions, tables and defined terms are left out of the count. Results under rules like these will differ from a general-purpose checker, so for a compliance test, follow the counting method the rule specifies.

What readability formulas can’t tell you

A formula only sees sentence length and word length. It can’t tell whether your ideas come in a sensible order, whether a short word is one your reader knows, or whether a sentence is grammatical at all: “Dog the ran fast” scores as very easy. Use the score to find sentences worth a second look, then read the text aloud. For length and timing, the reading time calculator and word counter fill in the rest.

Frequently asked questions

What is a good Flesch Reading Ease score?

For most writing meant for the general public, 60 or higher, which Flesch's scale calls plain English. Scores of 70 and up read easily for most adults. Academic and legal writing often lands between 30 and 50.

What does the Flesch-Kincaid grade level mean?

It estimates the US school grade a reader needs to understand the text. A score of 8.0 means an eighth-grade reader should follow it. It was derived in 1975 for the US Navy from tests with 531 enlisted personnel.

How is the Flesch Reading Ease score calculated?

206.835 minus 1.015 times the average words per sentence, minus 84.6 times the average syllables per word. Shorter sentences and shorter words both raise the score.

Why do different readability checkers give different scores?

They use the same formulas but count sentences and syllables differently. Abbreviations, headings, numbers and unusual words are the usual causes. Expect a few points of difference between tools.

How can I improve my readability score?

Split long sentences, especially any over about 25 words, and swap long words for shorter ones where the meaning stays the same. The checker lists your longest sentences and most-used long words so you know where to start.

Is my text uploaded anywhere?

No. The checker runs in your browser, so nothing you paste is sent to a server.