The use of readability formulas is best understood in the context of creating considerate texts. A text is easy-to-read when it matches the reader's reading ability, interest, motivation, and prior knowledge. We create considerate texts by keeping those features of the reader in mind.

Reading ability is usually determined by the level of one's education and reading habits. We should not think that all seventh graders can read a seventh-grade text. The reading skills of students in an actual seventh-grade classroom can go from the second to the 12^th grade. Many college graduates are not able to read at the 12^th-grade level.

The larger the audience, the less we know about its reading ability. When we look at the reading ability of adult population of the U.S., we find that the average person reads at the ninth-grade level. This means that many adults read at less than this level. When we have to reach the maximum audience, we have to write at two or three grades below that.

Comics are written at the fourth-grade level or lower. Most popular fiction is written at the sixth-grade level. Reader's Digest is written at the ninth-grade level, the New Yorker at the 10^th-grade level and newspapers at the 12^th-grade level. The target reading level for large, public audiences is the seventh grade.

What are the factors that determine one's reading level? The two most important factors are skills in understanding vocabulary and sentence structure. We improve our reading skills by learning to understand words that are more difficult and sentences that are more complex.

Educators use these two factors in testing the reading ability of students. We also use them to assess the reading difficulty of texts. Reading formulas (such as the Flesch Reading Ease formula) predict the difficulty of texts by measuring the average length of words and sentences.

Besides using a formula to test readability, you can also test your document with cloze tests on actual members of your audience.