In car stereos, the "DIN" marker indicates the dimensions of the in-dash stereo component, also referred to as the "head" unit. The single DIN is the standard measurement for a vehicle's audio system. It measures 2 1/8 inches long by 7 1/8 inches wide.
Aside from the single DIN, the other types of DIN sizes are the double DIN and the 1.5 DIN. The double DIN is currently the preferred car stereo size for most vehicle owners. It has twice the capacity of the single DIN in terms of height. One of the advantages of Double DIN car radios are pre-installed applications, such as Bluetooth, smartphone integration and navigation system.