The purposes of this study were to develop normative maximum grip strength (GRIP) data for men and women aged 20 to 64 years, separated into nine five-year age groups, and to develop prediction equations for GRIP using gender, age, height, weight, and hand dominance. A total of 1,182 volunteers (553 men and 629 women) participated in the study. Maximum hand grips were obtained using the Jamar dynamometer with standardized positioning and instructions. The hand to be tested first was chosen randomly. Each hand was then tested alternately. Three trials were performed on each hand. The highest GRIP for each hand was used for analysis. Two-way analyses of variance showed significant differences between the right and left hands and across the age groups for both genders. Follow-up analyses showed that significant decreases occurred between the age groups of 50-54 and 55-59 years in men and between the age groups of 50-54 and 60-64 years in women. The data also indicated that right and left GRIPs were highly correlated with each other (r = 0.93). Gender, height, and weight moderately correlated with both GRIPS (r = 0.52-0.73. Age correlated weakly with both GRIPs (r = -0.17). If either the right or the left GRIP was known, the other GRIP could be predicted easily from the known GRIP, with 87% of variance accounted for. Without the knowledge of the other GRIP, either GRIP could be predicted through gender, height, weight, age, and hand dominance, with 61% to 62% of the explained variance. The norms and prediction equations of GRIP developed in this study for men and women aged 20 to 64 years will help clinicians with decision making regarding grip strength.