In very round numbers:
7 billion on the earth today with about 1 billion in the Americas, 1 billion in Europe and Russia, 4 billion in Asia, and 1 billion in Africa.
By 2050, Asia is supposed to add a 5th billion and Africa a 2nd billion for 9 billion total.
By 2100, Africa is supposed to add a 3rd and 4th billion for 11 billion total, after which it is supposed to level off.
Nigeria is #13 @ 5.25. Niger is number 1 at 6.89. Those fertility rates are at the CIA factbook, or UN, or World Bank. The CIA Factbook national fertility rate table is best because it is arranged in descending order and Singapore is at the bottom with 0.80.
No way any of that will happen. Africa is really barely holding on and without western aid it will sink. Asia is on the verge of a huge culling of the herd with war as is Europe.