The Rule of Five

To estimate the readability of a book that has no Lexile rating, try the following:

Primary teachers have used the “five-finger method” for years. Readers select appropriate reading levels by using the fingers of one hand to count down the number of unknown words on a single page. Any more than five unknown words means that the text is at your frustrational level and another book should be selected.*

To update and refine this technique for older students, reading texts that have about 5% of the words that are unknown to you is at the appropriate independent reading level. Reading this level of text will expose most readers to about 300 unknown words in 30 minutes of reading. Learning 5% of these words from the surrounding context clues of the text is realistic. This means that students will learn about 15 new words during a typical reading session.*

This does not, however, work well with technical or specialized text (like philosophy books, science books, text books, or technical manuals written for professionals). These books have specialized vocabulary that is often only used in that field. They require a different kind of reading (where the reader constantly monitors his or her understanding) than books we read for pleasure.

*adapted from Mark Pennington’s comments at


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