To compare

In the calendar year (to end of December 31st of year of release)
XY sold (Note: This was 2 and a half months) 11.61 million units
ORAS sold just under 10 million units
Sun & Moon sold 14.69 million units
USUM sold 7.17 million units
Let's Go sold 10 million units

— Joe Merrick (@JoeMerrick) January 31, 2019