Plant-to-plant variation for corn (Zea mays L.) forage-quality traits has not been adequately described. A field study was conducted for 2 yr, using hybrids with a range in maturation, each grown at two sites. Precipitation and temperature deviated considerably from normal in both growing seasons. Ten consecutive plants were harvested from each plot and separately analyzed for forage-quality traits. Differences among the forage-quality variables were consistent for the hybrid maturity groups, and data were pooled for analysis. When the product of variance × total cost was minimized, sample size was not greatly different for any of the measured variables when the cost ratio was low. If the cost per plot is 10 times that of the cost per plant, the product of variance × total cost is minimized at 9 plants plot−1 for whole-plant digestibility. When detection limits were considered but not costs, whole-plant digestibility was the least variable trait and grain proportion was the most variable trait among the traits measured. If a detectable difference of 20 g kg−1 in whole-plant digestibility between hybrids is desired, it would require sampling 4 plants plot−1, while a difference of 20 g kg−1 in stover digestibility could not be detected with an infinite number of plants per plot. Grain proportion explained a relatively small portion of the variation in whole-plant digestibility and was better related to stover-quality traits. Key words: Corn, maize, forage quality, variation, stover, grain