The use of Archimedes' principle in finding the volume of an object is to measure the volume of a fluid (usually water) when the object is immersed in the fluid. The volume of the fluid displaced is equal to the volume of the object. So assuming the sphere will sink in water, you would fill a calibrated container part full (so as to be sufficiently deep to completely immerse the sphere without spilling over), note the volume before immersing the sphere, immerse the sphere and note the change in volume.