The tie ratio for Halo 3 to the installed base is very similar to what it is in the US, from what data we have recieved. In the US, that's 53%.sp0rsk said:How much did Halo 3 sell in Europe? Surely not 3 million.
Last I read, NA 360 sales were about 2/3 of the WW total (put differently, the rest of the world is 1/2 what NA is.) It works out to be ~7.5m. 8.1 doesn't seem unreasonable at all.