The average American (2012 data) has an ecological footprint of 8.2 global hectares. 1 Ten billion Americans will create a footprint of at least 82,000,000,000 gha. This is 670% of the Earth's current biological capacity of 12,243,512,050 gha.
The world's current (2012 data) ecological footprint is 20,114,439,677 global hectares and the planet's biological capacity in terms of our current methods of using resources is 12,243,512,050 global hectares.
1 Global Footprint Network, "National Footprint Accounts," http://www.footprintnetwork.org/resources/data/.php/GFN/page/footprint_data_and_results/ (accessed June 1st, 2016).