Mathematically, there will be so many people on the planet in 2100. This has been argued by Jacqueline R. Kassun by using logical argument in what she refers to Mathemagical. The argument is the total square feet of Earth divided by the world population, which is declining will give approximately 1269 square feet per person.
Sorry, I can't answer you exactly, but I've heard that in only about 3000 years (if we keep reproducing at the rate we do now) earth would just be a giant blob, expanding out ward at the speed of light! :)
Well the earths surface area is 5,490,383,247,360,000 square feet so if each person took up one square foot that would be 5,490,383,247,360,000 people... Of course 70% of the world is water so 5,490,383,247,360,000 x 0.3 = 1,647,114,974,208,000 people :)