5 million pc
3 million ps4
2 million xbox one.... Maybe.

Probably not, though.

The first 2 games together sold more than 8 million copies. http://segmentnext.com/2014/09/05/witcher-witcher-2-sales-reach-8-million-mark/

I expect the game to sell four-five million on all platforms. The Witcher series was never known to be a big seller. I remember when console gamers used to criticize PC gamers for even listing the first game as a major exclusive. Things have certainly changed in the last seven years.

Two and a half million on PC, one million on PS4, one million on XBO.

It is above 2 million now. I think the total series is past 6 million. 

I wish vgc would update their numbers more T_T

But even then, like basically ~4-5 million (since it is one game) to 10 million is still quite a big jump

i doubt it will sell that much

My guess is more like 3 million for W1 (PC only), 5 million for W2 (PC, 360).

W3 will be the first franchise entry on 3 platforms. I think 8 to 10 million for W3 are doable (provided the game gets excellent ratings on all platforms). The majority of sales, 3.5 to 5 million, will be on PC. The real question is: How many PS owners will buy the game?

There's a site tha tracks Steam sales O.o

10m sounded way too high but after hearing its previous PC sales maybe its not.

I think 4-5m on consoles, and then 2-3m on PC, so still not quite. I think a fair number of previous PC sales will turn into console sales so I won't expect PC numbers to increase drastically

They do but it is wonky because they use their own method to track steam sales and not get it directly from valve! Think of them as the vgc of steam sales because there are a number of things that can affect the "sale" of a game. Also steamspy is in alpha so take it with a grain of salt