Taking the average for length (120 cm). The width of a capybara is surprisingly absent from the internet, so I had to improvise by counting pixels:
Finding a clean top-down photo was also surprisingly difficult, but I chose this one because it's laying fairly straight, and there's a visible prominence of its hip bone and spine. I don't want to count fur-fluff in the width, so multiplying the hip to spine count by two gets us a hip-to-hip count of 56 pixels, which is 0.209% of its 268 pixel length. Multiplying wiki's length average by 0.209 gets us a width of: 25.08 cm, x 120 cm gives us an area of 3,009.6 cm² (3.24 sq ft), or to make our units the same, 0.030096 km²
8,515,767 km² (Brazil) / 0.030096 km² (capybara) = 282,953,448.96 capybaras per Brazil
x 3 = 848,860,346.88 capybaras per 1 antarctic ozone hole!