Table 1. Readability Scales and Interpretation of Scores.

Scale	Formula	Historic use	Interpretation
Flesh-Kincaid grade level	(0.39 × [total words/total sentences]) + (11.8 × [total syllables/total words]) – 15.59	US military technical manuals	US grade of education required to understand a text on the first reading
Gunning Fog index	(0.4  ×  [total words/total sentences]) + (100 × [total complex words/total words])	Public newspapers	6: Sixth grade; 7: seventh grade; 8: eighth grade; 9-12: high school; 13-17: college; >17: college graduate
SMOG index	1.0430 (sqrt [complex words]  ×  [30/number of sentences]) + 3.1291	Health care materials	Years of formal education required to understand a text
Coleman-Liau index	(5.89 × [total characters/total words]) – (0.3 × [total sentences/total words]) – 15.8	US Office of Education textbooks	Years of formal education required to understand a text

Abbreviation: SMOG, Simple Measure of Gobbledygook.