PS4 : 108 million
Switch : 88 million
3DS : 74 million
Xbox One : I know that we're not supposed to have two different estimates, but it's a bit unfair that we don't know if Xbox One started with 26 mil the beginning of this year, or 30 mil this year. So i'll just say this :
If it's at 26 mil in the beginning of this year, than 51 mil. If it started at 30 mil than 56 mil.