Digital prototypes (DPs) allow designers to communicate design concepts to users by rendering physical characteristics of the concepts. To enhance user understanding of the concepts, it is important that the users be able to make better estimates of the values of the characteristics. Correctness of the estimates can depend on two crucial factors: the ability of DPs to render the physical characteristics and the way the DPs are used to communicate the physical characteristics. However, little attention has been paid to the latter. A DP can be used in different ways, e.g., it can be projected on different backgrounds, or be manipulated using different input/output devices. Hence, it is important to identify an effective way of using DPs, via an assessment of the effectiveness of various ways. This paper introduces a methodology for evaluating the effectiveness of communication of physical characteristics to users using DPs. The methodology is used to assess the degree to which users can correctly and quickly estimate the values of the characteristics through interactions with DPs. Such assessments are then analyzed with statistical methods and hypothesis tests to reveal the effectiveness. To validate the proposed methodology, the size of hand-held electronic consumer products, such as smartphones, is considered in a case study. In the study, the effectiveness of two communication setups is evaluated. The same DP is used in both setups, while the environments and input devices are different. The experimental results show that the evaluated effectiveness can reflect how successful the setups are, and can help select the best way of using the DP, i.e., by providing a better environment, a better input device, or a combination of both.