Estimating product life from laboratory or field test data is a frequently encountered problem. One popular approach to handling this problem is through the use of Weibull graph paper. However, the accuracy of prediction is difficult to determine, since it involves the engineer, the graph paper, and the statistical variability of the population.This paper presents the results of a study to determine the accuracy that can be expected in typical Weibull plotting and estimating situations. The study was based on designed experiments utilizing typical engineers to provide estimates. The results provide guidance in the selection of sample size and assessment of prediction accuracy.