The following formula is involved in the calculation of Pearson correlation coefficients from covariance values:

Pearson correlation coefficient:
where cov_{XY} is the covariance between X and Y, σ_{X} is the standard deviation of X, and σ_{Y} is the standard deviation of Y.

The following references can be used to cite this correlation coefficient calculator (from a covariance):
 Soper, D.S. (2015). Correlation Coefficient Calculator (from a Covariance) [Software]. Available from http://www.danielsoper.com/statcalc 
 Cohen, J., Cohen, P., West, S.G., and Aiken, L.S. (2003). Applied Multiple Regression/Correlation Analysis for the Behavioral Sciences (3rd edition). Mahwah, NJ: Lawrence Earlbaum Associates. 