Continent Area (km²) Approx. population 2008 Density People (per km²) Asia 43,820,000 3,879,000,000 86.70 Africa 30,370,000 922,011,000 29.30 North America 24,490,000 528,720,588 21.0 South America 17,840,000 382,000,000 20.8 Antarctica 13,720,000 1,000 0.00007 Europe 10,180,000 731,000,000 69.7 Australia 9,008,500 32,000,000 3.6 http://www.mapsofworld.com/world-continent-map.htm
Now just add up North america, south america, and europe and australia, and we get 1.6B people. This doesn't include asia, which we know they do sales per,
"We may still use China facilities for Pacific Rim distribution (South Korea, Japan, China, Thailand, Vietnam, etc). "
So 1.7B people plus the 3.8B people in asia, is 5.5B people.
So using your numbers, 2.5M sponges within 30 days, with 5.5B people, means that .0004, or .04% of these people need to buy just 1 sponge over 30 days.