The earth has a population of about three
billion people. Considering the huge number
killed during the Great Tribulation, if 1/3 are
wiped out under the Sixth Trumpet, it will
hardly leave one and a half billion.

The Vial judgments and Armageddon are yet
to come, and that indicates that less than a
billion people will be left by the time the
Battle of Armageddon is over.

These are rough estimates.