When we are writing English articles, essays, papers, stories, or any other English texts, we usually give a big attention to spelling and grammar. We try to be perfect on our writing. But, do you know that besides a text should have a perfect spelling and grammar it should be “readable” too?

There are some popular theories and tests about text readability. A readability test is important to measure how readable a text is. As we know, some texts are sometimes more suitable for university graduates while the others can be easily understood even by 7th graders!

Now, in this post I’d like to share some information about “Readability Indexes” that commonly used to test readability level of a text. You might be interested to know it, to re-check your texts, whether they are “easy to understand” or not.

Flesch-Kincaid. The Flesch/Flesch–Kincaid readability tests are readability tests designed to indicate comprehension difficulty when reading a passage of contemporary academic English. There are two tests; the Flesch Reading Ease, and the Flesch–Kincaid Grade Level. Although they use the same core measures (word length and sentence length), they have different weighting factors. The results of the two tests correlate approximately inversely: a text with a comparatively high score on the Reading Ease test should have a lower score on the Grade Level test. Rudolf Flesch devised both systems while J. Peter Kincaid developed the latter for the United States Navy. Such readability tests suggest that many Wikipedia articles may be “too sophisticated” for their readers. (Source:–Kincaid_readability_test)

flesch-kincaid reading easeGunning Fog. In linguistics, the Gunning fog index measures the readability of English writing. The index estimates the years of formal education needed to understand the text on a first reading. A fog index of 12 requires the reading level of a U.S. high school senior (around 18 years old). The test was developed by Robert Gunning, an American businessman, in 1952. The fog index is commonly used to confirm that the intended audience can read text easily. Texts for a wide audience generally need a fog index less than 12. Texts requiring near-universal understanding generally needs an index less than 8. (Source:

Dale-Chall. The Dale–Chall readability formula is a readability test that provides a numeric gauge of the comprehension difficulty that readers will have when reading a text. It uses a list of words that groups of fourth-grade American students could reliably understand, considering any word not on that list to be difficult. (Source:

dale-chall readibility formulaColeman-Liau. The Coleman–Liau index is a readability test designed by Meri Coleman and T. L. Liau to gauge the understandability of a text. Like the Flesch–Kincaid Grade Level, Gunning fog index, SMOG index, and Automated Readability Index, its output approximates the U.S. grade level thought necessary to comprehend the text. (Source:

Automated Readability Index (ARI). The Automated Readability Index (ARI) is a readability test designed to gauge the understandability of a text. Like the Flesch-Kincaid Grade Level, Gunning Fog Index, SMOG Index, Fry Readability Formula, and Coleman-Liau Index, it produces an approximate representation of the US grade level needed to comprehend the text. (Source:

Simple Measure of Gobbledygook (SMOG). The SMOG grade is a measure of readability that estimates the years of education needed to understand a piece of writing. SMOG is the acronym derived from Simple Measure of Gobbledygook. It is widely used, particularly for checking health messages. The SMOG grade yields a 0.985 correlation with a standard error of 1.5159 grades with the grades of readers who had 100% comprehension of test materials. (Source:

To test your text, you can use some free services from the sites below:

I have also tried to test one of my published articles here. I tested “HOW TO IMPROVE YOUR ENGLISH LEARNING EXPERIENCE WITH FIREFOX ADD-ONS” and here are the results:

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