Smog Index - Readability

Readability is all about how you deal with reading. Do you find it easy to read through papers or articles? Or do you find it difficult with long sentences and words with unknown meanings? Readability involves what you see as you read, like the font size, the text presentation, the colors used, etc.

In the business world, readability is very important

Good readability is supposed to draw the reader in and help them learn from what they are reading. If writing is hard to comprehend and tedious, readers will simply move on to easier material. If you look at a product and the description is filled with high-tech jargon, you may lose interest and decide to not purchase that item.

Grading measures like the Smog Index help a lot with this

Certain grading measures can assess the literacy levels needed to understand a text. One of these measures is the SMOG index. Simply put, the index measures your education level with your writing level and determines the age required to understand a text. It's based on the reading level of a particular age group.

SMOG stands for Simple Measure of Gobbledygook

The SMOG Readability Formula is widely used to work out the correct reading age for a piece of writing by looking at its degree of readability. You can also use the SMOG calculator for the calculation of grade-level reading scores. It’s an online tool that is easy to use. All you need do is type or paste the text into the input to get your results.

The SMOG Readability Score doesn’t assess text for little kids, though

The SMOG Index starts with 4th grade in the USA. In the UK, Wales, and Australia, that is the equivalent of Year 5, when children are about 9 and 10 years old. At this age, the SMOG Readability Formula can be used as a readability formula to find out how suitable writing is for a specific grade level.

Who discovered the SMOG Readability Score?

A man named G. Harry McLaughlin developed it. He was an editor at the UK’s Daily Mirror newspaper. When he left the Daily Mirror he completed a Doctorate in Psycholinguistics and then went on to teach at universities in Canada and the UK.

It was while he was at Syracuse University in Canada that he published his SMOG formula in 1969 using statistical analysis. He specifically developed this formula as a simple measure of readability so he could work out what level of education a person would need to understand certain texts that had been written.

People doubted his formula in the beginning

People were cynical about it, especially those in the academic world – they didn’t believe it could work. But it was discovered that the formula produced accurate results using readability metrics and went on to be used widely afterward. It is now the preferred method to assess the level of readability of health-related texts.

How does it all work though; this SMOG Readability Score?

The SMOG Readability Score was designed for analyzing texts that contain thirty sentences or more and was designed to analyze text in English. Remember that other languages will have different rules and word structures, so SMOG works only for English.

When you calculate your SMOG score, there are a couple of things you need to take note of:

  • That a long sentence that is divided with a semicolon is counted as two sentences.
  • That hyphenated words are counted as single words.
  • That proper nouns are counted if they’re polysyllabic (polysyllabic means three syllables or longer). If the same polysyllabic word appears more than once in the text, it should be counted as a separate word each time it appears.
  • That numbers need to be counted if they are written as words and are polysyllabic.

SMOG is particularly used in the health sector

It is preferable that healthcare manuals and health information materials should be written at either 5th or 6th-grade reading levels [1]. Studies have shown that most Americans read at those grade levels. There are benefits of using readability formulas like these in the healthcare industry for the language of customer health:

  • Readability formulas ensure healthcare professionals can read and understand documentation and instruction manuals of medical equipment, such as X-ray machines, ultrasound machines, dental chairs, etc.
  • Patients need to know their conditions as well as the drugs they use, the advantages and disadvantages of treatments, etc. This is accomplished by communicating with patients through health information materials, which can involve written documentation, verbal instructions, and more.
  • Did you know that low health literacy skills affect patients? Often, adults with low literacy skills have a poorer health status. They often experience higher health costs and also seem to have trouble sticking to their medication schedules and understanding their illnesses.

It is vital to have clear doctor-patient-pharmacist communication

If patient instructions are beyond their reading capabilities, they are unlikely to follow them. If the pharmacist can’t understand the doctor’s prescription, there is a possibility that the wrong medication gets dispensed. With the help of readability formulas, healthcare professionals can avoid unnecessary confusion.


SMOG is a simple measure that assesses the years of education needed to understand a text. Doctors in the UK have been told to write ‘plain English’ to their patients, which means using shorter sentences and avoiding high medical jargon that nobody but the doctor can understand.

Patients used to have to figure out medical exchanges about their illnesses between medical specialists and a GP. Now, doctors write directly to their patients using plain English. There is no doubt that SMOG has gone a long way in making a positive impact by improving readability in the NHS and other places in the world.

All Readability Tests:

Here is a list of all readability tests.

Jonathan Gillham

Founder / CEO of I have been involved in the SEO and Content Marketing world for over a decade. My career started with a portfolio of content sites, recently I sold 2 content marketing agencies and I am the Co-Founder of, the leading place to buy and sell content websites. Through these experiences I understand what web publishers need when it comes to verifying content is original. I am not For or Against AI content, I think it has a place in everyones content strategy. However, I believe you as the publisher should be the one making the decision on when to use AI content. Our Originality checking tool has been built with serious web publishers in mind!

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