A common metric unit of area. One square kilometer equals 100 hectares, 106 square meters, approximately 247.105 acres, or approximately 0.386 102 square mile
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}