The Powers-Sumner-Kearl Readability Formula is one of the best formulas to
calculate the US grade level of a text sample based on sentence length and number of
syllables. This formula is suited for primary age children (age 7-10) and, usually, is not
considered ideal for children above the age of 10 years. The Powers-Sumner-Kearl
Readability Formula is attributed to an article,
A Recalculation of Four Adult
Readability Formulas in 1958 in the
Journal of Educational Psychology, University
of Wisconsin, by
R D Powers,
W A Sumner, and
B E Kearl.
Sumner and Kearl recalculated the
Gunning Fog Index Formula using the
McCall-Crabbs Reading Lessons. The newly revised Gunning Fog Index Formula was:
Grade level = 3.0680 + .0877
(Average Sentence Length) + .0984 (Percentage of
Monosyllables)
