Car stereos are made up of 2 parts: the head unit which we interact with, and the speakers which transmit audio from the head unit to us. As the main source of entertainment during our drives, technology has advanced from cassette players to modern touchscreens that we can interact with. Many head units used to come with a CD player and USB support, which is obsolete now that head units have smartphone integrations or have built-in services.
There is a standard for car stereos sizes, called DIN (Deutsches Institut für Normung), meaning the German Institute of Standardisation. The standard originated from Germany and was then adopted worldwide as ISO 7736. There are 2 main sizes, namely Single din and Double din, but carmakers have also come up with their own proprietary head units.
Single din head units measure at 2*7 inches (51*178mm), and their rectangular shape is more prominent in cars from the 90s till early 2000s. They are small and don’t take up much space, but have limited functionality compared to Double din, and are commonly fitted with a knob along with various buttons and a tiny display.
Double din head units are double the height of Single dins, measuring at 4*7 inches (102*178mm), and are easy to differentiate from Single dins as they look more like a square. Because of the added real estate they are often packed with more features, the most common being the addition of a touchscreen display and reverse camera view.
Since a standard for head units is present, swapping your head unit out for aftermarket ones is a simple task. All you need to do is determine if you have a single din or double din, and you can find an abundance of them available online. You can then choose to DIY it if you have the knowledge, or bring it to a car accessory store to let them do the work for you.
It is also possible to install a single din in head units designed for double din, although not recommended as it will leave an empty space in your head unit. If your head unit looks like it doesn’t follow the global standard, do not fret as it might just be a housing for single or double dins, or in the off chance that it is actually a manufacturer proprietary head unit, there will surely be aftermarket head units designed for your particular model that can be swapped in easily.