Readability Tests and Formulas

by Kalli Bravos | Jan 14, 2010

Flesch Reading Ease

Flesch Reading Ease = 206.835 - (1.015 * (Words / Sentences)) - (84.6 * (Syllables / Words))

Score Notes
90-100 Very Easy (Easily understood by an average 11-year old student)
80-90 Easy
70-80 Fairly Easy
60-70 Normal (Easily understood by 13 to 15 year old students
50-60 Fairly Difficult
30-50 Difficult
0-30 Very Difficult (best understood by college graduates)

Flesch-Kincaid Readability Test - Wikipedia, the free encyclopedia

Flesch Kincaid

The Flesch Grade Level Readability Formula (Flesch Kincaid) is an enhanced version of the Flesch Reading Ease. It was created by Rudolf Flesch and Co-Authored by John P. Kincaid. This version returns a Grade Level. 

Flesch–Kincaid = (0.39 * (Words / Sentences)) + (11.8 * (Syllables / Words)) - 15.59

Flesch-Kincaid Readability Test - Wikipedia, the free encyclopedia

Gunning Fog

The Gunning Fog Index was developed by Robert Gunning in 1952. The index is an indication of how many formal years of education one requires to comprehend the text.

Gunning Fog = 0.4 * ((Words / Sentence) + 100 ( Complex Words / Words))

A Complex Word has three or more syllables, not including proper nouns, familiar jargon or compound words, or common suffixes such as -es, -ed, or -ing as a syllable.

Gunning fog index - Wikipedia, the free encyclopedia


The Coleman-Liau Index is a readability test designed by Meri Coleman and T. L. Liau in 1967. Similar to the ARI it is based upon characters instead of Syllables. 

Coleman-Liau Index = (5.89 * (characters / words)) - (29.5 * (Sencences/Words)) - 15.8

Standard Formula

Simplified Formula

Coleman-Liau Index - Wikipedia, the free encyclopedia


Focuses on functional literacy, questionnaires, forms, text that is not in narritive form. Readability is determined on the number of single syllable words (not number of sentences and their length). Formula is strictly not to be used for assessing primary age reading materials.

GL = 20 - (N/10)

(Based on a sample text of 150 words)
GL = Grade Level 
N = Number of monosyllabic words in the sample text.


Fry Graph

It is sometimes used for regulatory purposes, such as in healthcare, to ensure publications have a level of readability that is understandable and accessible by a wider portion of the population.

1. Randomly select three separate 100 word passages. (Count every word including proper nouns, initializations, and numerals.) 
2. Count the number of sentences in each 100 word sample (estimate to nearest tenth). 
3. Count the number of syllables in each 100 word sample. (Each numeral is a syllable. For example, 2007 is 4 syllables and one word.) 
4. Plot the average sentence length and the average number of syllables on the graph. 
5. The area in which it falls is the approximate grade 

Fry readability formula - Wikipedia, the free encyclopedia

New Dale-Chall

Based on the average sentence legnth and the number of unfamiliar words (words not in the Dale-Chall Familiar Word List). Normally used to assess upper elementary through secondary materials. One of the most accurate Readability formulas.

RGS = (0.1579 x DS) + (0.0496 x ASL) + 3.6365

RGS : Reading Grade Score 
DS : Dale Score, or % of words not on Dale-Chall list of 3,000 common words 
ASL : average sentence length (the number of words divided by the number of sentences)

Score Notes
4.9 - Grade 4 and Below
5.0 to 5.9 Grades 5 - 6
6.0 to 6.9 Grades 7 - 8
7.0 to 7.9 Grades 9 - 10
8.0 to 8.9 Grades 11 - 12
9.0 to 9.9 Grades 13 - 15(College)
10 + Grades 16 +(College Graduate)


The Powers-Sumner-Kearl Formula is a revised Gunning Fog Index. Most often used in evaluating text indended for use in primary grades (up to the third grade level) and is based on words, syllables and total number of sentences.

GL = 0.0778(ASL) + 0.0455(NS) – 2.2029 

GL = US Grade Level 
ASL = Average Sentence Length
NS = Number of Syllables
(Sample Passage of around 100 words)


SMOG (Simple Measure of Gobbledygook)

Unlike any of the other formulas, SMOG predicts the grade level required for 100% comprehension. Designed as a substiture for the Gunning Fog Index, based upon syllables. Used primarily for checking Health Messages. The result is a grade level.

Standard SMOG Formula

Adjusted SMOG Formula

SMOG =1.043 * SQRT(30 X PollySyllables / Sentences) + 3.1291

SMOG - Wikipedia, the free encyclopedia


Similar to the Dale-Chall Formula, as it used a list of familiar words, but used for third grade and below.

Original Formula
GL = (0.141 * ASL) + (0.086 * PDW) + 0.839

Revised Formula
GL = (0.121 * ASL) + (0.082 * PDW) + 0.659 

(Based on sample 100-150 words)
GL = U.S. grade level
ASL = Average sentence length
PDW = Percentage of Difficult Words

Unfamilar Spache Word List

Spache Readability Formula - Simple English Wikipedia, the free encyclopedia

Automated Readability Index (ARI)

Designed to gauge the understandability of a text, output correlates to the US Grade level needed to comprehend the text. Relies on characters rather than syllables.

As Tailored for the US Army
GL = 0.50 (words per sentence) + 4.71 (strokes per word) – 21.43

As Tailored to Navy
GL = .4 (words per sentence) + 6 (strokes per word) – 27.4

The Principles of Readability - William H. DuBay
Automated Readability Index - Wikipedia, the free encyclopedia


Requires 400 tokens (word and math tokens)
Formula I
Predicted Readability = .23X - .53Y + 61.88

Formula II
Predicted Readability = -0.15A + 0.10B -0.42C - 0.17D + 35.52

A = words not on Dale list 
B = number of changes from word token to math token and vice cersa
C= number of different mathematics symbols not on the 80% mathematics list plus # of different math symbols not on the 90% Symbols list
D = Number of Question Marks
X = number of mathematics words no on the 80% mathmematics list
Y = number of different words with three or more syllables 

Unfortunately, I was unable to find the mathematics or symbols list.

Kane, R. B., Byrne, M. A., & Hater, M. A. (1974). Helping Children Read Mathematics. New York: American Book Company.
Handbook of reading research By P. David Pearson, Rebecca Barr, Michael L. Kamil, Peter B. Mosenthal

Bormuth Index

Based on a count of characters rather than syllables. The formula was designed to evaluate more academic documents (ie school textbooks). Uses the Dale-Chall Familiar Words List

Bormuth Grade Level = .886593 - (AWL x 0.03640) + (AFW * .161911) - (ASL x 0.21401) - (ASL x 0.000577) - (ASL x 0.000005)

BGL : Bormuth grade level score or Bormuth readability score
AWL : average word length or number of characters per word (number of characters divided by the number of words) 
AFW : average familiar words per word (the number of words in the original Dale-Chall list of 3,000 simple words divided by the number of words) 
ASL : average sentence length in words or average number of words in sentence (number of words divided by the number of sentences) 

Also called Degrees of Reading Power (DRP), but uses a slightly adapted Formula

Readability = .886593 - .083640(Letters/Words) + .161911 (DLL / Words)^3 - 0.021401(Words/Sentences) + .000577 (Words/Sentences)^2 - .000005(Words/Sentences)^3
DRP = (1 - Readability) * 100
DLL = Dale Long List words

Bormuth Grade Level Readability Score, other reading scores
Handbook of reading research By P. David Pearson, Rebecca Barr, Michael L. Kamil, Peter B. Mosenthal
The Principles of Readability - William H. DuBay

Raygor Readability Estimate

The Raygor Estimate Graph is a readability metric for English text, developed by Alton L. Raygor (1977). The U.S. grade level is calculated by the average number of sentences and number of long words ( >= 6 characters). These averages are plotted onto a specific graph where the intersection of the average number of sentences and the average number of letters/word determines the reading level of the content. Note that this graph is very similar to the Fry Readability Formula's graph. This graph is primarily used in secondary education to help classify teaching materials and books into their appropriate reading groups.

Use a 100-word passage from the selection. Use multiple if passage is long
Count the number of sentences in each passage. Count a half sentence as .5. 
Count the number of words in each passage containing six or more letters. 
Find the point on the Raygor Estimate Graph.

Raygor Readability Estimate - Wikipedia, the free encyclopedia

Linsear Write

Linsear Write is a readability metric for English text, purportedly developed for the United States Air Force to help them calculate the readability of their technical manuals. The result is the approximate Grade level of the writing.

(Easy Words + (Hard Words * 3) / Sentences
Hard Words have 3 or more syllables
Easy Words have 1 or 2 syllables
If answer > 20 then divide by 2
If answer <=20 subtract 2 then divide by 2
Based on 100 word sample

Linsear Write - Wikipedia, the free encyclopedia

Strain Index

Strain Index, which is based on the following assumptions:
1. The longer the sentence, the greater the strain.
2. The standard sentence has 17 words.
3. All syllables are equal ('ash', 'lash', 'slash' and 'splash').

The Strain Index can be calculated in three easy steps:
1. Choose the first three sentences.
2. Count the number of syllables in the three sentences (S3).
3. Divide S3 by 10.

Score Notes
5.1 and Under very easy to read
15.3 and Over very difficult to read


McAlpine EFLAW (c) Rachel McAlpine 2004, updated 2006.

The McAlpine EFLAW Readability Score, developed by Rachel McAlpine, is based on two significant flaws: long sentences and a high proportion of miniwords. Both these flaws bamboozle EFL readers.

EFLAW = (Words + MiniWords) / Sentences

1. Count the words (A) 
2. Count the miniwords (Miniwords are short, common words of one, two or three letters) (B) 
3. Count the sentences (C) 
4. Add (A + B) and Divide by (C) 
5. The result is the EFLAW(tm) Score

Score Notes
1-20 very easy to understand
21-25 quite easy to understand
26-29 a little difficult
30+ very confusing

From Plain English to Global English - Rachel McAlpine
McAlpine EFLAW Readability Score « Readability Monitor


The Huerta Reading Ease is a Modified Flesch Reading Ease for Spanish Texts.

Huerta Reading Ease = 206.84 - (0.60 * P) - (1.02 * F)

(Using 100 word chunks of text)
P = Number of syllables per 100 words
F = Number of sentences per 100 words 

How is the Huerta Reading Ease score calculated? 

A user has submitted a "correction" to the Huerta Reading Ease formula. You can find it at Linguist List. Thanks to Gwillim Law of Measurement, Inc. for pointing this out.

Laesbarhedsindex (LIX) (Leesbaarheid)

The Lix formula, developed by Bjson from Sweden, is very simple and uses a mapping table for its scores. It is useful for documents of Western European languages. It has been successfully used on, English, German, French, Greek and Sweedish. The score is based on sentence length and the number of long words (long words are words over six characters). The formula used to calculate the Lix index is:

Lix = ( words / sentences ) + 100(words >= 6 characters / words)

Score Notes
0-24 Very easy
25-34 Easy
35-44 Standard
45-54 Difficult
55+ Very difficult

Generating and Rendering Readability Scores for Project Gutenberg Texts - Ronald P. Reck & Ruth A. Reck
Analysing the readability of English and Non-English Texts in the Classroom with Lix - Johnathan Anderson


Very Similar to the LIX, as it can be used on documents of most Western European Language, but easier to calculate.

RIX = (Long Words / Sentences)

(long words = words where number of characters > 6)

Ratio Grade Level
7.2 and above College
6.2 and above 12
5.3 and above 11
4.5 and above 10
3.7 and above 9
3.0 and above 8
2.4 and above 7
1.8 and above 6
1.3 and above 5
0.8 and above 4
0.5 and above 3
0.2 and above 2
Below 0.2 1

Readability Index - Thomas Jakobsen and Thomas Skardal
Read-X: Automatic Evaluation of Reading Difficulty of Web Text - Eleni Miltsakaki & Audrey Troutt

Hayashi / Tateisi et al.

For Japanese, the critical factors are: sentence length, length of runs of Roman letters and symbols and of the different Japanese characters (Hiragana, Kanji and Katakana), and the ratio of tooten(comma) to kuten(period). The original formula used 10 factors, the following is only based off of six.

Readability Score = -(0.12 * LS) - (1.37 * LA) + (7.4 * LH) - (23.18 * LC) - (5.4 * LK) - (4.67 * CP) + 115.79

LS = length of the sentences
LA = average number of Roman letters and symbols per run 
LH = average number of Hiragana characters per run 
LC = average number of Kanji character per run 
LK = average number of Katakana character per run 
CP = ratio of tooten (comma) to kuten (period)
Run = a continuous string of the same type of character

Readability Formulas -- TxReadability from The Accessibility Institute
Automatic Assessment of Japanese Text Readability Based on a Textbook Corpus - Satoshi Sato, Suguru Matsuyoshi, Yohsuke Kondoh


An Adapted Flesch Reading Ease tailored for Dutch

Reading Ease = 206.84 – (0.77 * ( Syllables / Words)) – (0.33 * ( words / Sentences))

Sentence Accents and Stuttering Frequency in Dutch - Anke Geudens & Jo Verhoeven
Ethnic minorities and Dutch as a second language - Guus Extra & Ton Vallen

Kandel & Moles

A Modified Flesch Reading Ease tailored towards french text.

Reading Ease = 209 – (0.68 * ( Syllables / Words)) – (1.15 * ( words / Sentences))

Writing to be read: Readability indices for Open Educational Resources - Griff Richards