Some number crunching:

Domestically Infinity War had a 2.63 mutiplier. China had a 1.88 multiplier. The rest of the overseas total had a 2.63 multiplier.

Translate that to Endgame, and you get 941 domestic and 2.95b total.

Now I don't expect it to be able to have the sane hokds with such a huge opening. But if you go for a baseline of 2x mulipluer you get 716 domestic and 2.42b worldwide.. I think it's reasonable to suppose it will land somewhere between those two numbers