Just as there will be for the men's match on the same night, there will be 30 entrants in the women's Royal Rumble.
WWE clarified some of the specifics for the women's Rumble in the opening segment of Raw tonight. Kurt Angle announced that it would have the same rules as the men's match, with there being 30 entrants, eliminations occurring when a wrestler goes over the top rope and both feet touch the floor, and the winner getting a title shot at WrestleMania.
With there being enough active women on the Raw and SmackDown rosters (without counting the champions) to account for a bit more than half of those 30 wrestlers, it appears that the rest will be from NXT or other surprise entrants.
Naomi, Asuka, Ruby Riott, and Natalya have been officially confirmed for the women's Royal Rumble. The pay-per-view takes place at the Wells Fargo Center in Philadelphia on January 28th.