Sometimes the manufacterer will provide such information if you gve them all the details, incuding, counterweight, boom lentgh, radius, loads, etc.
Otherwise it can be approximated. Shaperio has an excellent rigging book that explains how to do this. Most crane manufacterers do not provide enough data to directly calculate, so you may need to make some educated assumptons about weight distribution in certian components of the crane. It is a calculation that requires some time to do. For large cranes working at close raius, the controlling loads may be the back outriggers with no load in the falls. Picking over a corner may be the most stable configuration, but it too may generate your controling load. Best bet is to consult the manufacterer or a rigging engineer.
