Archive for December, 2007

Simple Flesch Grading

December 19, 2007

By Nirmaldasan

Rudolph Flesch is famous for his Plain English campaign. Yet his name is associated with readability formulae that are far from plain. If AWS is the average words per sentence; and ASW, the average syllables per word —

* FRE (Flesch Reading Ease) = 206.835 – 1.015AWS – 84.6ASW

* FKI (Flesch-Kincaid Index) = 0.39AWS + 11.8ASW – 15.59.

The FRE scale ranges from 1 to 100: higher the score, simpler the text. A text that tests 90 and above is suitable for the fifth grade. The FKI is an attempt to grade the FRE on a scale of 1 to 17. In this scale, the score indicates the grade-level of the text: the higher the score, the more difficult the text. For example, a score of 11 indicates that the text is suitable for the 11th grade.

These formulae, with its decimal points, intimidate writers rather than compel them to test their writing with a formula. Though Davis Foulger made a successful attempt to simplify the counting procedure, his ‘A Simplified Flesch Reading Ease Formula’ is equally complex. His article is available online at

My argument is that any formula for Plain English must be plain, simple and beautiful. Without mincing words, I present that simplification:

SFG (Simple Flesch Grading) = (AWS/10) + 10(ASW – 1) 

For grade-conversion, I used the formula 13 x [1 – (FRE/100)] + 4. The actual result ran into several decimals and looked complicated. But I found that an approximation looked simple and compelling. And I called it Simple Flesch Grading. But how reliable is the SFG?   

Instead of testing the formula on actual texts, I substituted possible values for the variables AWS (5, 10, 15, 20, 25, 30, 35, 40) and ASW (1, 1.5, 2, 2.5, 3, 3.5, 4). I do understand that all these combinations are not equally likely. I have tabulated the results for FRE, FKI and SFG. Please take a look at the table at

The relationship between these formulae is shown by the Pearson’s product-moment correlation: – 0.927942 (FRE and FKI); – 0.98567 (FRE and SFG); 0.90755 (FKI and SFG). The correlation indicates that SFG is a reliable indicator of readability.