We evaluated the precision of 5–60‐min electrofishing samples for estimating relative abundance of largemouth bass Micropterus salmoides and developed guidelines for optimizing sample duration so that catch rates may be estimated precisely and with the least effort. Catch per hour in the study reservoirs ranged from 16 to 98 and was independent of sample duration. However, the variation in catch per hour among samples of equal duration increased as catch rate and sample duration decreased, resulting in the need for more samples. The total effort (i.e., time spent electrofishing, traveling between sample sites, and processing fish) needed to estimate a mean catch rate with specified precision was a function of sample duration, catch per hour, and travel time. More effort was needed as catch rate decreased and travel time increased, but the relation between sample duration and total effort was parabolic. Short‐duration samples (5 and 10 min) generally resulted in greater total effort as catch rate decreased and travel time increased. In contrast, although more samples were needed, short‐duration samples resulted in less total effort when travel time between sample sites was shorter than about 30 min. Long‐duration samples (50 and 60 min) were more efficient only when travel time was long and catch rates were low. Samples of intermediate duration were generally the least efficient.