Australia is the largest country located entirely within the Southern Hemisphere. Its mainland, Tasmania, and principal external islands all lie south of the Equator, and the country covers about 7.69 million square kilometres.
Australia stretches from tropical waters near its northern coastline to temperate and cool regions in the south. Its size makes it the sixth-largest country in the world by total area, after Russia, Canada, China, the United States, and Brazil. Despite its vast territory, most Australians live near the coast, especially around Sydney, Melbourne, Brisbane, Perth, and Adelaide.
Brazil is a common trick answer because it is the largest country by land area in the Southern Hemisphere overall. However, Brazil crosses the Equator, so it is not entirely within that hemisphere. Indonesia also spans both hemispheres, while South Africa and Argentina are wholly or almost wholly south of the Equator but much smaller.
Australia is also unusual because it is both a sovereign country and the principal political entity occupying an entire continent. Its Antarctic claim is treated separately and is not needed for this geographic comparison.