Originating Person

Calculating Readability

Readability research began in 1920’s


Gray and Leary (1935)

5 key elements of the text:

# of different hard words in a 100-word passage

# of first, second, and third-person pronouns

average sentence length in words

percentage of different words

# of prepositional phrases

Rudolf Flesch (1948)

Flesch Readability Formula”

Count words, syllables, and sentences in three 100-word passages.


Reading Ease = 206.835 –  84.6 (total syllables/total words) – 1.015 (total words/total sentences)


Results fall between 1 and 100, and the researcher looks it up on table (low numbers mean hard reading level; 64 is considered plain English).

Robert Gunning (1952)

“Gunning Fog Index”

2 key elements (in 100-word passage):

Average Sentence Length in words (asl) = 100/number of sentences (treat a fragment as a whole sentence)


Hard Words (hw) = # of 3-or-more-syllable words/100 words (discount proper nouns, easy combinations like “newsletter”, familiar jargon, and verbs in which suffix –ed, -es, -ing forms the third syllable.


GFI (grade level)  = (ASL + HW) * 0.4


Online Calculator: http://gunning-fog-index.com/

Wilson Taylor (1953)

“Cloze Procedure”

Questioned assumption of above formulae that short words are easier to understand.  In his procedure, the researcher deletes every x words (i.e., every 5th word) then gives the mutilated passage to a test group, who must fill in the blanks.  Scoring is done by counting the number or percentage of blanks correctly filled in: the higher the number, the easier the reading.

Powers-Sumner-Kearl Readability Formula (1958)

Best used for children under age 10.  Select 100-word passage, Count number of words and divide by number of sentences to get Average Sentence Length (ASL).  Count the number of syllables and divide by number of words to get average Number of Syllables per Word (NS).  Use formula:

US Grade Level = 0.07778(ASL) + 0.0455(NS) – 2.2029.


Online calculator: http://www.readabilityformulas.com/free-powers-sumner-kearl-test.php

Automated Readability Index (ARI) (1967)

Uses characters/word instead of syllables/word.  A character is considered any letter, number or punctuation mark. The formula is:


Grade Level = 4.71 (characters/words) + 0.5 (words/sentences) – 21.43


Online Calculator:


G. Harry McLaughlin (1969)

“SMOG - Simple Measure of Gobbledygook”

Take at least 10 sentences in a row, count the number of words with 3+ syllables.


Grade Level = Ö number of words of at least 3 syllables * (30/number of sentences)         + 3


Online Calculator: http://www.wordscount.info/hw/smog.jsp

Flesch-Kincaid (1975)


Count words, syllables, and sentences in three 100-word passages.


Grade Level = 0.39 (total words/total sentences) + 11.8(total syllables/total words) – 15.59


Online Calculator: http://www.standards-schmandards.com/exhibits/rix/


Merri Coleman and T. L. Liau (1975)

“Coleman-Liau Index”

Take any medium-length passage:

Grade Level = (5.89 * characters/words) − (0.3 * # of sentences in 100-word fragment) − 15.8

Online Calculator:


Lexile Framework for Reading (1980s)

Based on word frequency and sentence length.  Results range from 0L to over 2000L, with higher numbers indicating more difficult text.  The analysis is proprietary, but if you know a child’s lexile reading level or you want a book in a particular Lexile, you can use the site called “Find a Book”: http://www.lexile.com/fab/ 

Edward Fry (1988)

“Fry Readability Graph”

2 key elements (select three 100-word passages in book):

average # of syllables in 100-word passage

average # of sentences in 100-word passage


Look up results on graph.

Zakaluk & Samuels (1988)

Based on 4 key elements:

 - two “outside the head factors”

      - text readability level

      - “adjunct comprehension aids” (i.e., subheadings)


- two “inside the head factors”

      - word recognition skill

      - knowledge of the text topic

Linsear Write Formula

Developed by the US Air Force to analyze their technical manuals, this formula counts the number of “hard” (3+ syllables) and “easy” (< 2 syllables) words.  The formula is:


(# of easy words) + (3 * # of hard words)/number of sentences.  If result is > 20, divide by 2 for grade level.  If number is < 20, subtract 2, then divide by 2 for grade level.

List of other readability calculations


Other online calculators

http://www.readabilityformulas.com/free-readability-formula-tests.php   (calculates: Flesch Reading Ease, Gunning FOG, Coleman-Liau index, Flesh-Kincaid Grade Level, ARI (Automated Readability Index), SMOG, Linsear Write Formula)