The purpose of this study was to determine the accuracy of using relative muscular endurance performance to estimate 1 RM bench press strength. College students (184 men and 251 women) were tested for 1 RM strength following 14 weeks of resistance training. Each subject was then randomly assigned a relative endurance load (rep weight) corresponding to 55–95 percent of the 1 RM and required to perform as many bench press repetitions (reps) as possible in one minute. Men had significantly greater 1 RM strength, rep weight, percent 1 RM, and reps than women. Since the regression of percent 1 RM on reps was not significantly different between the men and women, the data were combined to produce the following exponential equation: percent 1 RM = 52.2 + 41.9e −0.055 reps (r = 0.80, p < 0.001). Bench press strength could be estimated from the equation 1 RM = rep weight/predicted percent 1 RM/l00 with an accuracy of r = 0.98 and a standard error of estimate of ± 4.8 kg. Applications of these equations to a comparable cross-validation group (70 men and 101 women) indicated acceptable validity (r = 0.98, p < 0.001) with an error of only ± 5.4 kg. Applying the same equations to high school male athletes (n = 25), high school male nonathletes (n = 74) and college football players (n = 45) also produced good cross validation (r > 0.95, p < 0.001) with relatively small standard errors (± 3.1 to ± 5.6 kg). It appears that relative muscular endurance performance can be used to accurately estimate 1 RM bench press strength in a wide variety of individuals.