Try a Reading Index to Check Your Readability

What is a reading index? I’ve been asked that many times in the past. A reading index is a way to calculate writing to see if the text matches a reader’s grade level. This is also known as readability.

There are a number of reading indexes out there including Flesch-Kincaid Grade Level, Flesch Reading Ease, Gunning Fog Index, SMOG, Automated Readability Index, and more. If you use Word, you are probably familiar with Flesch-Kincaid Grade Level and Flesch Reading Ease. You can see this by using grammar and spell-check. If it doesn’t show up after you have used spelling and grammar, select it in the options (for the reading index) in the preferences and get the results for your document every time you run spelling and grammar.

Results from Word (for Mac) showing Flesch-Kincaid Grade Level & the Flesch Reading Ease

Rudolf Flesch worked on the Flesch Reading Ease in 1948 and later co-created the Flesch-Kincaid grade level in 1975 (Readable, 2021).

The Flesch-Kincaid grade level is calculated using a simple formula.

Flesch-Kincaid grade level formula

The Flesch-Kincaid Grade Level and Flesch Reading Ease are arguably the most popular reading indexes, although some organizations prefer using other choices such as the Gunning Fog depending on usage. The Flesch-Kincaid grade level is for overall general usage while some reading indexes are focused on other types of documentation such as education, healthcare, and business. The Gunning Fog is generally used for business and health (Boztas, 2017, et al.) as well as government.

While there are plenty of online reading index calculators, a writer can do the math themselves. The Gunning is calculated somewhat like the Flesch-Kincaid grade level.

Gunning Fog index calculation

A reading index is just another tool a writer can use, just like a spelling and grammar checker. Remember, it provides a method to calculate the complexity of written materials to match the intended audiences’ reading level. Be aware that reading indexes are useful but not perfect. Whatever formula you decide to use, a reading index is helpful if used correctly.


Boztas, N., Omur, D., Ozbilgin, S., Altuntas, G., Piskin, E., Ozkardesler, S., & Hanci, V. (2017, November). Readability of internet-sourced patient education material related to “labour analgesia.” PubMed Central (PMC).

Readable. (2020, November 10). The Flesch Reading Ease and Flesch-Kincaid Grade Level.

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