Spache (Revised) Readability Formula

The Spache (Revised) readability formula calculates the U.S. grade level of a text sample based on sentence length and number of unfamiliar words. Unfamiliar words are ones that do not appear on a specially designed list of common words that are familiar to most younger readers (4th grade and below).

Spache is generally used for primary age (Kindergarten to 7th grade) readers to help classify school textbooks and literature, whereas Dale-Chall is better meant for secondary age readers.

Because this formula is based on the usage of familiar words (rather than syllable or letter counts), it is often regarded as a more accurate test for younger readers.

Note that the Spache word list and formula were revised in 1974 and this is the version that Readability Studio uses.

The Spache Formula

GL = (.121 * ASL) + (.082 *UW) + .659

Where:

GL	U.S. grade level
ASL	Average sentence length
UW	Number of unique unfamiliar words

This test requires a 100-word sample; however, note that Readability Studio always analyzes your entire document to guarantee the most accurate results and does not use subsamples for any of its test calculations. If a formula requires a subsample of a specific size, then standardization is used.

Citations

Spache, G. (1953), 'A new readability formula for primary-grade reading materials', The Elementary School Journal, 55, 410-413.

Spache, G. (1974), Good Reading for Poor Readers.