How to Tell What Reading Level a Book Is

How do you determine the reading level of a book? This is one of the questions that frequently comes up for teachers, parents, and even authors who are concerned about ensuring that readers are engaging with content that is suitable for their current reading skills. Understanding reading levels is essential, especially for educators and parents who want to foster reading habits in children and ensure the material they choose challenges the reader without overwhelming them.

However, determining the reading level of a book isn’t a straightforward task. It involves a combination of quantitative data and qualitative judgment, often relying on established frameworks and testing methodologies that take into account vocabulary, sentence structure, themes, and other textual characteristics.

In this article, I will walk you through six popular methods for evaluating the reading level of a book. Each method offers a unique approach, and by the end, you'll be well-equipped to assess a book's readability using a combination of these techniques. Whether you're a parent choosing books for your child or a writer targeting a specific audience, understanding these methods will prove invaluable.

1. The Flesch-Kincaid Grade Level

This is one of the most widely used readability formulas. Developed in 1975, the Flesch-Kincaid Grade Level is designed to tell you what school grade level a reader should ideally be in to understand the text. It's especially popular in schools and educational settings. The formula uses two factors:

• Average sentence length (in words)
• Average number of syllables per word

Here’s the formula:
Grade level = (0.39 * ASL) + (11.8 * ASW) - 15.59

Where:
ASL = Average Sentence Length (the number of words divided by the number of sentences)
ASW = Average Syllables per Word (the number of syllables divided by the number of words)

A lower score indicates easier reading material, while a higher score signals more complex text. For example, Dr. Seuss’s “Green Eggs and Ham” scores around a grade 2 level, while “War and Peace” would score much higher.

2. Lexile Framework for Reading

The Lexile Framework for Reading is another popular tool, especially used by educators and librarians. Unlike the Flesch-Kincaid, Lexile measures both the complexity of the text and the reader's ability. The system assigns a Lexile score ranging from 200L (beginner reader) to 1700L (advanced).

To assess the Lexile level of a book:

1. A proprietary algorithm measures the difficulty of the text based on sentence length and word frequency.
2. The result is a Lexile score that is matched to a specific grade range, making it easy to align books with readers.

For instance, books like “Harry Potter and the Sorcerer’s Stone” have a Lexile score around 880L, whereas adult novels such as “The Great Gatsby” are scored higher, around 1070L.

3. The Dale-Chall Readability Formula

The Dale-Chall Formula focuses more on word familiarity. It recognizes that readers might struggle more with unfamiliar words than with sentence complexity. This formula compares the text's vocabulary to a list of 3,000 familiar words that are understood by most 4th graders. If a word isn’t on this list, it’s considered "difficult."

Here’s the formula:
Dale-Chall Score = (0.1579 * Percentage of difficult words) + (0.0496 * Average sentence length)

Like the Flesch-Kincaid, the higher the score, the more challenging the text. The formula has been found to be particularly effective in determining readability for elementary school texts, but can also be applied to more advanced works.

4. Gunning Fog Index

The Gunning Fog Index measures how many years of education a person would need to easily understand the text on their first reading. It considers two main factors: word complexity and sentence length.

The formula is:
Fog Index = 0.4 * (ASL + Percentage of hard words)

Here:

• ASL = Average sentence length
• Hard words = words with three or more syllables

The Gunning Fog Index is especially useful for adult reading material. For example, a typical New York Times article might score around 12-14 on the Fog Index, indicating it’s written for high school seniors or first-year college students.

5. SMOG Index

SMOG stands for “Simple Measure of Gobbledygook.” It estimates the years of education needed to understand a piece of writing. The SMOG formula is known for being relatively simple compared to other readability formulas.

Here’s the calculation:

1. Count 10 sentences from the text.
2. Count every word with three or more syllables.
3. Apply this formula:
   SMOG grade = 1.043 * sqrt(number of polysyllabic words) + 3.1291

This method is often used in health literacy to ensure patient instructions are easy to understand. For example, government documents or medical instructions are usually aimed for a SMOG score of 6-8, to ensure broad accessibility.

6. The ATOS Reading Level

The ATOS (Advantage-TASA Open Standard) is used widely in educational systems to match students with appropriate reading material. It’s based on the number of words, word difficulty, sentence length, and text length.

One of the main advantages of the ATOS system is that it not only provides a grade-level score but also considers the book's entire length, making it especially helpful for longer texts.

Additional Methods & Tools

• Accelerated Reader (AR): Often paired with ATOS, AR assigns a point value to books based on their difficulty and length.
• Readability Consensus: Some online tools, like Readable.com, aggregate several readability tests and present an overall readability score.
• Qualitative Assessment: Beyond numbers and formulas, qualitative factors such as themes, content, and reader engagement play a crucial role in determining whether a book is appropriate for a given audience.

Choosing the Right Method

There’s no one-size-fits-all when it comes to readability assessments. Depending on the context — whether you’re selecting a book for an advanced student, assessing a classic novel for classroom use, or ensuring your content is accessible to a broad audience — one method may be more suitable than another. For example, the Flesch-Kincaid or SMOG index might work well for everyday reading material, while the Lexile framework or ATOS could be better for aligning books to educational standards.

In conclusion, determining the reading level of a book requires a blend of science and intuition. By applying these formulas and tools, you can gain a much clearer understanding of whether a book is appropriate for your reader’s skills and needs. Ultimately, choosing a book should also take into account the reader's interests and the content's engagement level, as reading enjoyment is as important as comprehension.