What are Square Kilometers?
A square kilometer is the area of a square with sides 1 kilometer long, which is 1,000,000 square meters or 100 hectares. Australia covers about 7.7 million of them.
What are Acres?
An acre is 43,560 square feet, which is about 4,047 square meters. It was originally the amount of land a yoke of oxen could plough in one day.
The United States and United Kingdom still measure land in acres, but most of the world uses hectares, which fit neatly into the metric system. One hectare is about 2.47 acres.