With somewhat oblong diameters of NUMBER@1 -- NUMBER@2 km , and a mass estimated to be NUMBER@3 % of the total mass of the belt , `` Mass of NUMBER@4 Hygiea '' NUMBER@5 / `` Mass of Mbelt '' NUMBER@6 = NUMBER@7 it is the fourth largest object in the region by volume and mass .

NUMBER@4 Hygiea is the fourth biggest object in the asteroid belt , somewhat non-spherical with diameters of NUMBER@1 -- NUMBER@2 km and a mass estimated to be NUMBER@8 % of the total mass of the asteroid belt .
