Prediction: PS3 will reach 105 million units before the Wii

[TheSource]

Also, as a rule of thumb you can essentially take a system's peak year and multiply it by four to six to come up with a range for lifetime sales.

NES Peak = 11m ---> LTD = 62m (x5.5)

SNES Peak = 12m ---> LTD = 49m (x4)

N64 Peak = 9.4m ----> LTD = 33m (x3.5)

GC Peak = 5.4m ---> LTD = 22m (x4)

Wii Peak = 26m --> LTD of... 105m - 110m ? (x4 - x4.33)

GBA Peak = 18m --> LTD of 81m (x4.5)

DS Peak = 31m ---> LTD of 155m - 160m (x5 ish)

3DS Peak to date = 12m ---> Will do at least 50m

PS1 Peak = 21m ---> LTD of 103m (x5)

PS2 Peak = 22.5m --> LTD of 160m? (x7 - this is the major exception)

PS3 Peak = 15m --->  LTD of 90-95m? (x6-x6.5?)

PSP Peak = 16m ---> LTD of 80m (x5)

Xbox Peak = 7m ---> LTD of 25m (x3.5)

X360 Peak = 15m ---> LTD of 90m? (x6?)

Genesis Peak = 8m ---> LTD of 30m (x4?)

DC Peak = 2.5m ---> LTD of 10m (x4)

PS2 had essentially no competition in 2005-2006, and 2000-2001, for being the main console (PS1 / N64 were dead in both time frames, and Xbox, GC, DC were beaten to a bulp in these years) so it will end up around seven times it's peak year. Typically the stronger the competition the lower the multiplier, although in this generation the 6-8 year span between consoles is also expanding the multiplier. Wii had the market dominated really just in 2008, PS3 / X360 started to become viable in 2009 on, and PS2 was viable in 2006-2007. PS2 was also the only platform to dominate all three global markets. DS owned Japan from 2005-2008, DS / PSP split it in 2009-2010, and 3DS has owned it since. West was dominated by Wii only 2007-2009, X360 / Wii / PS3 have been at parity since, with PS2 dominant before 2006. PS2 dominated the global market from 2001-2005 essentially. PS1 struggled vs. SNES / Saturn in 1994-1996 in Japan, and against N64 in 1996-1997 in the US, and SNES / Genesis in 1995 in the US, and then lost momentum to DC / PS2 in 1999-2000 globally, so it really only had 1998 to itself, and thus ended up with a fairly similar multiplier to Wii. SNES was also caught in between, with Genesis doing well in the West from 1992-1994, and NES doing well in 1990-1991, and then PS1 / N64 doing well after 1996. NES was much more like PS2 with a longer run of dominance, hence the bigger multiplier. DS was also fairly dominant, given that 91m were sold in it's best three years.