By G. Harry McLaughlin

My readability formula SMOG estimates the years of education needed to understand a piece of writing. SMOG is widely used, particularly for checking health messages. Because I dropped reading research to become a clinical neuropsychologist decades ago, I did not know how popular SMOG had become until I recently Googled SMOG formula and got half a million hits!

SMOG was published in 1969 BC [Before Computers] so I made calculating a text’s readability easy by offering an approximate formula — count the words of 3 or more syllables in 3 10-sentence samples, estimate the count’s square root, and add 3.

To save you even that counting and calculating, I have collaborated with JAVA programming expert Alain Trottier to provide a free SMOG Calculator which instantly assesses an entire text, not just a sample. Try the service using this link:

You can even paste a link like the one here into your own html webpage: copy it from here.

Alternatively you can put a link to this page in your browser list of favorites or into a pdf file. More information is on Alain Trottier's SMOG Calculator webpage.

SMOG Calculator uses my precise formula which yields an outstandingly high 0.985 correlation with the grades of readers who had 100% comprehension of test materials. Here is the formula generalized for more than 30 sentences:

The standard error of the estimated grade level is 1.5159 grades, comparable to that of other readability formulae. For a pdf file of the original paper click G. Harry McLaughlin (1969) SMOG grading: A new readability formula. Journal of Reading, 12 (8) 639-646.

SMOG Calculator incorporates Trottier's Syllable Counter, which uses a dictionary to look up the syllable length of words. Because of this, SMOG Calculator counts syllables more accurately than any other readability program.

You may have seen SMOG conversion tables compiled by one Harold C. McGraw. They are slightly inaccurate because they are based on the approximate formula I offered for ease of calculation. Tables for texts of fewer than 30 sentences are statistically invalid as well, because the formula was normed on 30-sentence samples.

A sketch of how SMOG came to be devised was published in a recent Plain Language at Work Newsletter.

Trottier and I are developing developing an new aid to clear writing, called CLEAR. It will show precisely which words and which sentences in a text need adjustment to make reading easier for adults.

Users will type or copy text into a panel on the CLEAR interface. After a few seconds the text will be reproduced on a new page with each word color-coded to indicate the lowest educational level of adult readers expected to know the word (hence the acronym Color Labeled Ease for Adult Readers). Each sentence will be followed by a color-coded bar indicating its complexity and the educational level of adults who would find it acceptable.

Within a few months CLEAR will be available on the Internet without charge and with no advertising. It could be placed on any webpage at no charge by copying a free snippet of HTML, like that for SMOG.

My early plan for a readability formula for adults normed on the educational levels of magazine readers is described in Temptations of the Flesch and Proposals for British Readability Measures.

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Copyright (c) 2008 G. Harry McLaughlin. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.