The outside diameter of the BOLT's smart heating base is 3.75 inches. At this size, it is designed to fit into most standard North American vehicle cupholders, HOWEVER each car is different and exact cupholder sizes vary. The BOLT base has a depth of 1 5/8 inches before the handle begins to extrude from the body of the mug. So before you can be sure that the BOLT usb heated travel mug will fit into YOUR particular cupholder, you must measure both of these dimensions.