The Xbox One is a big console, there is no hiding this fact. But when you put it next to the PS4, you begin to understand how big it actually is. In fact, it reminds us of the first Xbox, as that console was also, quite large.
In the image above, you can see the PS4 sitting on-top of the Xbox One, courtesy of PCgamers.de. Even when placed next to the Xbox 360, the One is still quite large.
But does size really matter? To most gamers, probably not. Seeing that the Xbox One is a device that is designed to stay inside your AV cabinet, being portable is not an important attribute for the console.
Also, don’t forget that the PS4 has its power-supply built in, while the Xbox One has an external power unit.
There are likely loads of reasons why the console is so large, one likely being the need to keep all the components cool. Back when the Xbox 360 launched, it was plagued by defective units and seeing the size of the Xbox One, Microsoft likely spared no expense to keep the console from over-heating.
Source: PCgamers.de