Measuring Readability of Contexts

Posted: October 30, 2010 in TechStuff
Tags: , , , ,

I came across with this free tool over the net that measures the readability of any write-up or article. I think it can also be used as an assessment if your article is appropriate for a specific target audience that you want to reach. Go to Edit Central and test your articles/contexts.

I tried it myself and copy the texts from my other blog entitled “Bacolod Trip and Masskara Festival 2010” and it gave the following grades below:

Flesch reading ease score: 73.6
Automated readability index: 7.5
Flesch-Kincaid grade level: 7.2
Coleman-Liau index: 7.9
Gunning fog index: 10.6
SMOG index: 9.9

At first, I never really understand what does the data mean, so I googled what each index/measurement are driving in. See compilation below from Wikipedia:

SMOG Index

The SMOG Index is the approximate version of SMOG (Simple Measure Of Gobbledygook). SMOG can be calculated more accurately with the instant free online SMOG Calculator which uses the precise formula that yields a correlation of 0.985 with the grades of readers who had 100% comprehension of test materials. No other readability formula is believed to correlate so highly with its criterion.


To calculate SMOG

  1. Count a number of sentences (at least: 10 from the start of a text, 10 from the middle, and 10 from the end).
  2. In those sentences, count the polysyllables (words of 3 or more syllables).
  3. Calculate using

The result estimates the number of years of U.S. education needed to fully comprehend the text

Gunning Fog Index

Gunning fog index is a test designed to measure the readability of a sample of English writing. A fog index of 12 has the reading level of a U.S. high school senior (which is around 18 years old). The test was developed by Robert Gunning, an American businessman, in 1952.[1]

The fog index is generally used by people who want their writing to be read easily by a large segment of the population. Texts that are designed for a wide audience generally require a fog index of less than 12. Texts that require a close-to-universal understanding generally require an index of less than 8.


The Gunning fog index can be calculated with the following algorithm:[2]

  1. Take a full passage that is around 100 words (do not omit any sentences).
  2. Find the average sentence length (divide the number of words by the number of sentences).
  3. Count words with three or more syllables (complex words), not including proper nouns (for example, Djibouti), familiar jargon or compound words, or common suffixes such as -es, -ed, or -ing as a syllable.
  4. Add the average sentence length and the percentage of complex words
  5. Multiply the result by 0.4

The resulting number is a rough estimate of the number of years of formal education that a person requires in order to understand the text on a first reading.

Coleman-Liau Index

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.

Coleman-Liau relies on characters instead of syllables per word. Although opinion varies on its accuracy as compared to the syllable/word and complex word indices, characters are more readily and accurately counted by computer programs than are syllables.


The Coleman-Liau Index is calculated with the following formula:

L is the average number of letters per 100 words and S is the average number of sentences per 100 words.

Flesch–Kincaid Readability Test

The Flesch/Flesch–Kincaid readability tests are 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, so 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. Both systems were devised by Rudolf Flesch.

Flesch Reading Ease Formula

In the Flesch Reading Ease test, higher scores indicate material that is easier to read; lower numbers mark passages that are more difficult to read. The formula for the Flesch Reading Ease Score (FRES) test is

Scores can be interpreted as shown in the table below.

Score Notes
90.0–100.0 easily understandable by an average 11-year-old student
60.0–70.0 easily understandable by 13- to 15-year-old students
0.0–30.0 best understood by university graduates

Flesch–Kincaid Grade Level Formula

These readability tests are used extensively in the field of education. The “Flesch–Kincaid Grade Level Formula” translates the 0–100 score to a U.S. grade level, making it easier for teachers, parents, librarians, and others to judge the readability level of various books and texts. It can also mean the number of years of education generally required to understand this text, relevant when the formula results in a number greater than 12. The grade level is calculated with the following formula:

The result is a number that corresponds with a grade level. For example, a score of 8.2 would indicate that the text is expected to be understandable by an average student in 8th grade (usually around ages 13–14 in the United States of America). This page has the score of 11.7.

The lowest grade level score in theory is −3.40, but there are few real passages where every sentence consists of a single one-syllable word. Green Eggs and Ham by Dr. Seuss comes close, averaging 5.7 words per sentence and 1.02 syllables per word, with a grade level of −1.3. (Most of the 50 used words are monosyllabic; “anywhere”, which occurs 8 times, is an exception.)

  1. woah! nosebleed… penge tissue… argg.. math itoh… :)) pakiexplain nga in lay man’s term…

    • bloggerokuno says:

      Hahahaha…sige para sa’yo Ms. Pakitongkitong 🙂

      The article above only shows the computation. No need to do it yourself. As I’ve mentioned there’s a free tool already – Edit Central.

      And to give you a brief explanation…

      SMOG, Gunning fog, Coleman-Liau index are results representing the number of years in (US) education that an individual has to take to understand a context. Like in the article I tested, it simply implies that a high school student can easily comprehend the article.

      While with Flesch reading ease score of 73.6, referring back to the table above, an individual with age starting 11 year old, will have the capability enough to understand the message of the article.

      Hope I shed you light on this. Thanks!

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