Glomerular filtration rate (GFR) is an important clinical indicator of kidney function. It can be used as an independent predictor of long-term survival after cardiac surgery. Definition, methods of measurement, and corrected value by body surface area are briefly introduced in this paper. Details of the calculation of estimated GFR (eGFR) by Levey's formula with serum creatinine, age, gender, and race are offered. The relationship between estimated GFR and the four factors is shown graphically and discussed. An eGFR/creatinine conversion table for individual patients derived from the eGFR equation with clinically significant cutpoints is given, which can be used by physicians as a pragmatic reference.