During injection molding, the cooling process generally consumes more than 50% of the total processing time. Therefore, the cooling efficiency is typically improved by optimizing the cooling channel arrangement. However, it takes significant time to optimize and is challenging to apply to mold design. A quantitative design methodology that efficiently generates a cooling circuit within a short period was developed. First, a cooling-channel design equation was derived based on a simulation of the heat transfer process in the mold to express the relationship between the diameter, depth, and distance of the cooling channel. Next, the design equation was used to plot a cooling-channel design graph by applying PP, ABS, PC, and PMMA, materials widely used for injection molding. Finally, the cooling channel was generated by applying this graph to the shape of the actual automotive bumper, and the cooling analysis was performed. The proposed method demonstrates an efficient cooling-channel design.