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Readability Guidelines to Calculate Readability Scores by Brian Scott

What is a readability score?

A readability score is the grade level which readers need to read and understand your document.

First, let's look at the pros and cons of using readability formulas on text.

The advantages of readability formulas:

1) Measure what grade level a person must have completed to read a text.

2) Are text-based.

3) Are easy to use.

4) Do not need real readers to measure your text.

5) Can identify if a text will be too complex for your readers.

Readability formulas cannot:

1) Tell you if a person will understand or has the skills to interpret the text.

2) Dissect the meaning of a word or measure the complexity of a word or phrase.

3) The readability measurements that formulas provide are purely quantitative.

Basically, readability formulas will help you answer the following question about a document: "Will I be able to read this text if I have an X-grade reading level?"

Common Readability Formulas

The Fry Graph

The Fry Graph is a commonly used readability assessment tool. You can see an example of the Fry Graph at

Here is how you can calculate a readability grade level using the Fry Graph.

1. Select three 100-word passages.

• Ideally one passage from the beginning, middle, and end.

• Do not count acronyms, numerals (e.g., 1, 2, 3), or Web sites.

2. Count the number of sentences in each passage.

3. Count the number of syllables in each passage.

• Short cut: Each word has at least one syllable; therefore, skip the first syllable and count the additional syllables. Take this number of syllables and add 100 (to account for the first syllables).

• Every syllable of every word should be counted regardless of how many times a word is repeated throughout the passage.

4. Average the number of sentences and syllables.

• Special cases: If you have more than 100, but fewer than 300 words, in a document, then count the total number of sentences and syllables in that document. Divide the number of sentences and the number of syllables by the total number of words in the document. Multiply by 100. The results are the approximate averages of sentences and syllables. Continue to Step 5.

5. Find the corresponding number set (coordinates) on the Fry Graph available at

• Use the grade-level table (not age in years).

• The number of sentences is on the x-axis and the number of syllables is on the y-axis.

• NOTE: Extend the lines to estimate the reading level of outliers.

• If a number set is on a line, then identify both grades. For instance, 7.3 sentences and 148 syllables would be grade level 7/8.

SMOG (Statistical Measure of Gobbledygook) Formula

The SMOG Formula is used less frequently than the Fry Graph, but many organizations still use it. You can find an example of the Smog Formula at


1. Use the SMOG Formula for documents with 30 or more sentences.

2. Select three 10-sentence passages from the document.

• Ideally, select one passage from the beginning, middle, and end.

3. Count the number of "big words" in each passage. The Smog Formula considers big words as words with three or more syllables.

• If you see a big word repeated three or more times in a single 10-sentence passage, count the word only once per each 10-sentence passage.

For example:

The word "demonstrator" is repeated four times in the first 10-sentence passage; you should count it once. In the second 10-sentence passage "demonstrator" is repeated twice; therefore, it you should count it twice. In the final 10-sentence passage, "demonstrator" is repeated three times; therefore, you should only count it once. In this example, "demonstrator" accounts for four of the big words in the document.

4. Find the corresponding grade level on the SMOG conversion table available at

A third type of readability formula is the Fog Index (sometimes referred to as Gunning-Fog). The Gunning Fog Index measures the readability of English writing. The Index estimates the level of education (or grade level) one needs to understand a text on the first reading.

Here is how to calculate the Gunning Fog Index:

1. Use for documents with fewer than 30 sentences.

2. Count the total number of words in the document.

• Do not count acronyms, numerals (e.g., 1, 2, 3), or Web sites.

3. Count the number of big words, words with three or more syllables, in the document.

4. Count the number of sentences in the document.

5. Calculate the average sentence length (words in a sentence) in the document. Divide the total number of words by the total number of sentences.

6. Calculate the percentage of big words in the document. Divide the number of big words in the document by the total number of words in the document and multiply by 100.

7. Add the average sentence length and percentage of big words together (the values calculated in steps 5 and 6).

8. Multiply the sum by 0.4. The final result is the Fog Index or grade level.

9. For an example of a Fog Index calculation go to

How to Choosing a Readability Formula

1. You should use two readability measurements to calculate the reading level for a document.

2. Use the Fry Graph calculation for each document, regardless of length.

3. Depending on the length of the document, use either the SMOG Formula or Fog Index calculation.

• For longer documents (30 or more sentences), use the SMOG Formula calculation.

• For shorter documents (fewer than 30 sentences), use the Fog Index calculation.

4. Average the Fry Graph and SMOG Formula/Fog Index readability measurements together.

5. Be advised: Fry Graphs are more forgiving -- the Fry Graph will calculate a lower reading score compared to the reading level calculated by the SMOG Formula or Fog Index.

• Re-check your calculations if the Fry Graph and SMOG Formula/Fog Index reading levels are different.

6. Figure out a system to reduce miscounting. For example:

• Use a colored pen.

• Block off each passage that you need to measure with a line or a box. Note: you may find it easier to measure similar sections of the document for the SMOG Formula/Fog Index and Fry Graph. Obviously the length of the passage that you take from the section will be different (For a Fry Graph it will be 100 words, and for a SMOG Formula it will be 10 sentences).

• Put a dot over every multiple syllable (not counting the first syllable). Then put a strike through the syllable after you have counted it.

• Go back and circle each word that has at least two dots over it (these are the big words).

Which documents should you measure for readability?

• Any document intended for the public.

• In-house professional guides and other technical materials not intended for the general public do not have to be measured.

NOTE: You should always measure readability on any material that you distribute to the public.

• You might have several documents that need separate reading level measurements within a single resource. For example:

A pet health education manual has five newsletters, three fact sheets, a story, and two questionnaires. If the newsletters are in a series, you can treat them as a single document. Therefore, the pet health education manual requires 7 Fry Graph and SMOG Formula/Fog Index calculations (1 for newsletters + 1 for each fact sheet (3) + 1 for the story + 1 for each questionnaire (2) = 7).

• When in doubt, do the count: If you are unsure if readability is necessary, go ahead and perform it. It is better to remove a reading level calculation than to calculate it later.

Brian Scott is a contributing writer for Lousy Writer where he helps writers and non-writers how to write better.

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