Three-dimensional (3D) product design is an essential ability that students of subjects related to product design must acquire. The factors that affect designers’ per- formance in 3D design are numerous, one of which is spatial abilities. Studies have reported that spatial abilities can be used to effectively predict people’s performance in conducting complex operations. Nevertheless, few studies have explored the relationship between spatial abilities and designers’ performance in 3D product design. Spatial ability is a type of mental ability and comprises numerous factors. Carton box design is a typical type of standardized 3D product design, in which designers’ performance is affected by the spatial abilities they possess. The most crucial factor among these abilities is the space conversion ability, which is the ability to convert two-dimensional (2D) surface devel- opments into 3D perspective views and convert 3D carton boxes into 2D plans. These operations require an in-depth perception of objects, an understanding of the relative spatial relations among objects, and spatial visualization. In this study, carton box design was used as an example to investigate, using structural equation modeling, the effects that the ability to understand spatial relations, spatial orientation, and spatial visualization have on designers’ performance in 3D product design. The results indicated that all three spatial abilities (i.e., understanding spatial relations, spatial orientation, and spatial visualization) directly influence designers’ performance in carton box design. Therefore, spatial abilities are vital factors affecting designers’ performance in 3D product design.