Spache Readability Formula

If you want a method of discovering how hard a piece of writing is to read, you will find the Spache Readability Formula does that. The Spache will compare words that are in the text to words on a specific list that are familiar to the reader. If the word is not found on the list, it is classified as an unfamiliar word.

The Spache Readability Score is geared toward a certain age group

The Spache Readability Score is best used for English texts. They are specifically aimed at 4th-grade students and lower grades. It is not the best readability metric tool when it comes to general readability.

To use this formula, you first count the number of words in a sentence. The number of words and the percentage of unfamiliar words receive a score from the Spache Readability Formula. The result achieved is an estimate of the reading age that the particular piece of writing is suitable for based on its difficulty level.

The Spache Readability formula works best on texts for children under the age of 8 years.

Check out the formula here:

(0.141 * average sentence length)+(0.086 * percentage of difficult words)+0.839 = grade level

The Oleander Software Solution revised Spache Formula is:

GL (U.S grade level ASL = (.121 * ASL (average sentence length) + (.082 *UW (number of unique unfamiliar words) + .659

How to apply the formula

The Spache Readability Formula seems relatively straightforward, but many find it tedious to do. Here are the steps:

o Step 1: You need to choose a sample passage that is about 100-150 words long.

o Step 2: Count up all the words in the text.

o Step 3: Next, count all the sentences in the text.

o Step 4: Then divide the answer you got from Step 2 by the answer you got from Step 3 to get the average sentence length (or ASL).

o Step 5: Then count all the words in the text that are not found on the Spache word list.

o Step 6: Divide the answer you got from Step 5 by the answer you got from Step 2. Multiply by 100 and this will give you the percentage of difficult words (or PDW).

Why did George Spache introduce the world to the Spache Readability Score?

The Spache Readability Formula was designed by George D. Spache and introduced in 1952. He designed it to work best on texts for children up to the 4th grade.

It features a word list and this allows people to compare the words they find difficult in a text with the word list. The word list will provide an easier word that the child at the 4th-grade reading level will understand.

For older children, it is recommended that the Dale-Chall readability formula is used. In 1952, there was a new readability formula introduced for primary-grade reading materials. It is called The Elementary School Journal. It’s been revised since back then.

The Spache Readability Score considers two important factors

o Sentence length

o Specific words used

Some texts can be pretty long, but the original Spache Readability Formula only needed text to be around 100-150 words. Now, with modern technology around, people use automated means to cover an entire page or however long an article or text is.

In 1978, a revised version of the Spache word list was created

This is the version that is still used today - although it will probably be revised again in the future. It was Spache himself who believed that readability formulas should not be static and should be revived and revised with the times.

How do you improve your Spache Readability Score?

In order to score well on the Spache Readability Scale, your best bet is to use simple words. If you find checking the word list for other words too tiring, you can always use the Spache Readability Calculator. Here is the free Spache word list in a text file.

Spache Readability Calculator: this will help you to grade your text after you have used the Spache Readability Formula.

Why were these readability formulas developed?

Interest was sparked in adult education back in the 1930s during the Great Depression. Adults at this time were complaining that they wanted to read and learn more. But some adult books were difficult to read, making them inaccessible. Studies focused on what books were readable for adults.

The University Of Chicago Press started analyzing certain factors when people read books. They looked at:

o Content

o Format

o Style

o Structure

During the 1940s, many linguists tried to create an easy and reliable readability formula. Rudolf Flesch was the pioneer of adult readability formulas. He published his readability formula, calling it the Flesch Reading Ease. If the score was high, the test was easy to read. This formula was used in the public and private sectors.

In the 1950s, Robert Gunning also came up with his reading formula. George Spache followed up with his US grade-level Spache formula. He focused on ensuring that children’s text was age-appropriate.

The bottom line is that the linguists wanted to create reading formulas that were plain and simple, and that’s what they achieved. As a result, readability became an essential metric of reading ability. The plain language movement [1] started in the 1960s.

Which is the best readability test?

The best readability tool is one that uses several reliable formulas. It should also reflect modern language and literacy rates and include styles in its analysis.


George Spache created his Spache Formula in response to many previous frameworks being formulated for adults. It was Spache who saw a neglected age group that needed to be accounted for: children below the 4th-grade level.

It has become useful for parents to know what books have an appropriate rating for their child's readability level. You can also imagine how invaluable Spache has become for teachers because it quickly and accurately tells them if a text is likely to be understood.

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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