The question, as stated, cannot be answered sensibly. A square mile is a measure of area, with dimensions [L2]. A kilometre is a measure of distance, with dimensions [L]. The two measure different things and basic dimensional analysis teaches that you cannot convert between measures with different dimensions such as these without additional information.
517 square miles = 1,339.024 km2
516.9 square miles
About 517 square miles.
The area of Derventa is 517 square kilometers.
The area of Eungella is 517 square kilometers.
832 kilometers (517 miles)
The area of Sør-Odal is 517 square kilometers.
The area of Jõhvi Parish is 517 square kilometers.
The area of Illuka Parish is 517 square kilometers.
89063160.517 mi (.517 mi = 910.9 yd)
It is 517 kilometers from Hamilton, Ontario to Ottawa, Ontario.
517 miles = 832.030848 kilometres