Determine the Difficulty of Text Using Readability Formula

How do you know how difficult a text is to understand? One way, often recommended by teachers and professors, is to use a readability formula. These easy-to-use formulas estimate the reading level or grade level needed by readers.

Calculating the readability formula is a helpful tool for evaluating texts. However, you must use it with care.

What Is a Readability Formula?

A readability formula is a scientific model which assists in determining the difficulty of a text. The formula was created to find the most efficient ways to write in a simple and accessible way.

The formula uses several variables to find the best combination of tone and vocabulary. Conditions such as the number of words, sentence lengths, and the number of phrases are taken into account to determine the most appropriate readability.

It groups text into levels of reading difficulty. It evaluates what type of writing needs to be deviated from to make reading easier.

Importance of Readability Formulas

When writing for your students or any audience, your text must be as accessible and easy to read as possible.

A readability formula can help you determine whether your text is easy to read and understand or if it requires some extra assistance.

Many different types of texts exist in various genres like articles, books, brochures, and more. Some are written for a very specific audience, some are meant to be read by the general audience. Others are meant to be read by children. These texts have different readability scores.

Therefore, readability formulas have great importance to the writers. They can determine the writing level necessary to make text readable.

boy wearing gray vest and pink dress shirt holding book
Photo by Ben White on Unsplash

How Does Different Readability Formula Work?

The readability formula consists of the following parts: words, syllables, sentences, and characters. The quality of a text is decided based on how simple or difficult it is to read.

One of the primary purposes of these formulas is to help determine text quality for accessibility. The application varies depending on what you want to do. They can be applied in different settings, such as learning, teaching, or client-based tasks.

Some of the most common readability formulas are as below:

Flesch Reading Ease

The Flesch Reading Ease measures the readability of a test by assigning a number between 1 and 100.

Reading a text is easier with a higher score. Any score between 70 and 80 represents a grade 8 reading level which means the text is easy to grasp for an average adult.

The formula for the Flesch Reading Ease score:


While most readability formula indicates a lower score as easier to read, the Flesch-Kincaid formula is the opposite. A higher score means more straightforward text.

The Flesch-Kincaid grade level score indicates the US grade level education a person must have to comprehend a specific text. Flesch-Kincaid Grade Level 8 text requires someone to complete eight years of education and reach eighth grade to understand it.

The formula to calculate the Flesch-Kincaid Reading Level score:

0.39 x (Average Sentence Length) + (11.8 x Average Syllables Per Word) – 15.59.

The formula is an amended version of the Flesch Reading Ease, developed in1970s by US Navy for ease of usage. They used it to calculate the readability of technical manuals in training.

SMOG Index

SMOG, the abbreviation of Simple Measure of Gobbledygook, is a readability framework. The formula was developed by sampling a text of 30 sentences, so it is best for text over 30 sentences.

Psychologist G. Harry McLaughlin developed this formula. It estimates the years the education any average person must have to understand a piece of text.

The SMOG grade is suggested to be calculated on a piece of 30 sentences or longer considering the following:

  • Counting a total of 30 sentences with10 sentences from the beginning, middle, and end each.
  • Counting complex words with three or more syllables.
  • Rounding the result to the nearest 10 after square-rooting the number.
  • Adding three to the result to determine the final reading level.

Gunning Fog Index

The Gunning Fog formula assigns a score between 0-20 which determines the education level needed to comprehend a text.

The formula to calculate Gunning Fog Level score:

0.4 [(words/sentences) + 100 (complex words/words)]

Eighth-graders easily digest a text of Fog score 8, and anything above 17 is aimed for graduate-level understanding.

Dale-Chall Formula

The Dale-Chall formula assigns a number based on the readability of content. It works using a list of simple and monosyllabic words that a fourth grader can comfortably read.

The formula to calculate the Dale-Chall readability score:

0.1579 × (100 × total difficult words ÷ total words) + 0.0496 × (total words ÷ total sentences)

The lower the test score, the more familiar the words to a fourth grader and the easier the text. The key aspect of this readability assessment is word familiarity.

Wrapping Up

The effectiveness of text discussion is determined mainly by the relative difficulty of the text. The difficulty is identified by various formulas, including Flesch, Flesch-Kincaid, SMOG, and Gunning Fog Index.

Each formula is tailored to a specific level, and each calculation requires readers to assess text based on a certain language level. Generally speaking, the lower the language level, the more complex the text is.

By using a readability formula, students can determine which text is more appropriate for a particular level or audience.

Pam is an expert grammarian with years of experience teaching English, writing and ESL Grammar courses at the university level. She is enamored with all things language and fascinated with how we use words to shape our world.

What is Reading? — Making Sense of Letters and Symbols

When studying the English language, you should familiarize yourself with its different concepts. It includes spelling, vocabulary, grammar, and reading.…

July 4, 2022

What is Readability Score? — a Quick Guide

Your text should cater to all kinds of readers. When you’re writing an article that intends to reach various individuals,…

July 4, 2022

Causes of Reading Comprehension Problems

Reading comprehension is the ability to understand and interpret written words, connecting the information in the text with previous knowledge.…

July 4, 2022

What Is ZPD Reading Level?

Everyone unique and we all have a unique understanding of the world. So what should the level of difficulty be…

July 4, 2022

The Best ELL Strategies for Reading!

Non-native English speakers can be proficient readers in their original tongue. However, those who are enrolled in an ELL (English…

July 4, 2022

These Are the Best Practices in Reading!

Best practices have been a topic of discussion in the reading education community for a long time. Among these best…

July 4, 2022