There's no easy answer when it comes to deciding how many inches your recessed lights should be. It ultimately depends on the size of the room, the type of lighting you want and the overall aesthetic you're going for.
If you have a small room, 4-inch recessed lights may be all you need in order to create the desired effect. However, if you're looking for more light or a more dramatic look, 6-inch recessed lights may be a better option. Ultimately, it's up to you to decide what looks best in your space.