International standard ISO 7736 defines a standard size for car audio head units. The standard was originally established by the German standards body Deutsches Institut für Normung as DIN 75490, and is therefore commonly referred to as the "DIN car radio size". It was adopted as an international standard in 1984.

Head units generally come in either single DIN (180 x 50 mm panel) or double DIN (180 x 100 mm panel) size. The depth is not standardized; as a result, some cars such as the Opel Manta / Ascona have the correct sized front aperture but will accommodate few DIN sized radios other than the original due to the shallow depth; this despite the vehicle being manufactured as late as 1988. The US standard for a DIN radio is 2" x 7" and the Double DIN sized radio is a 4" x 7". Some radios in Japanese Kei cars do not conform to the DIN standard however.

Uniden Bearcat BCT-15

Blaupunkt Hamburg MP57

Single DIN spacer pocket

Rack braces and screw mounts exposed for single DIN installation

Double DIN combining a single DIN head unit and a single DIN compact disc player