arcgis desktop - Defining the appropriate Projected Coordinate System

I am a beginner at ArcGIS and have a technical question.

I need to assign a projected coordinate system to my boundary/polygon data in order to calculate square miles. There are many to choose from. Which should I be using? Here are my geographic coordinate system details:

Angular Unit: Degree (0.017453292519943295) Prime Meridian: Greenwich (0.000000000000000000) Datum: D_North_American_1983 Spheroid: GRS_1980 Semimajor Axis: 6378137.000000000000000000 Semiminor Axis: 6356752.314140356100000000 Inverse Flattening: 298.257222101000020000

Thanks in advance for any consideration.