A square kilometer, or square kilometre, is a unit of area. It is the size of a square that is one kilometer on a side. It is 1 million square meters, 100 hectares, about 247 acres, or about 0.386 square miles.
A square inch is a unit of area. It is the size of a square that is one inch on a side. It is 1/144th of a square foot, or exactly 6.4516 square centimeters.