The following formula is involved in the calculation of effect size values for multiple regression studies:

Cohen's f^{2} effect size for an Ftest:
where R^{2} is the squared multiple correlation.

The following references can be used to cite this effect size calculator for multiple regression:
 Soper, D.S. (2015). Effect Size Calculator for Multiple Regression [Software]. Available from http://www.danielsoper.com/statcalc 
 Cohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences (2nd Edition). Hillsdale, NJ: Lawrence Earlbaum Associates. 