(REUTERS/Lucy Nicholson)

Ever wonder why the World Cup is such a huge event? It’s because the target market for just the countries in the knockout round approaches over 1.1 billion people — the total population for the 16 teams remaining in the 2014 World Cup.

Among the countries in the round of 16, the United States boasts the largest population (319 million), roughly 100 times Uruguay, the smallest (3.3 million).

When Costa Rica takes the pitch against Greece you can bet a large portion of the 15.5 million people from both nations combined will be watching to see which surprise winner will be moving on to the quarterfinals. Those two countries also have the smallest difference of population between the knockout round matchups (six million).

The largest difference in population? United States over Belgium, where Team USA looks to count on more than 308 million more fans to believe they will win.