None.
A kilometre is a measure of length or distance in 1-dimensional space while an acre is a measure of area in 2-dimensional space. The two measure different things and, according to basic principles of dimensional analysis, conversion from one to the other is not valid without some addition information.
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1 million acres = 4046.856 sq km (to 3 dp).
1 million square feet = 22.96 acres.
1 million (square meters) = 247.105381 acres.
1 million (square meters) = 247.105381 acres
1 km = 1000 meters, so 1 million meters = 1000 km