For three-layer cardboard boxes, the thickness is typically set at around 3.5mm, while for five-layer boxes, it's about 7mm. We can determine the standard cardboard box specifications by first measuring the dimensions of the items to be stored according to relevant standards, then adding the thickness of the cardboard. This results in the exterior box standards. When ordering custom boxes, it's crucial to clearly specify to the manufacturer whether you need the interior or exterior box standards.