Twenty players are allowed to dress for an NHL game: 18 skaters and 2 goaltenders. This is the game roster that can actually take part in play, distinct from the larger group of players a club may carry under roster rules.
The 18 skaters are normally divided among four forward lines and three defensive pairings, although coaches can adjust those combinations during a game. Two goaltenders are dressed so one can start and the other can serve as the backup. Only six players per team are on the ice at once during normal play: five skaters and one goalie.
The number 23 is often confused with the game roster because it has traditionally referred to the maximum number of players on a club’s active roster during much of the regular season. Not all of those players necessarily dress for every game; healthy scratches remain available to the team but watch from the press box.
Injuries, emergency recalls, salary-cap rules, and special league provisions can affect the broader roster. The standard answer for players dressed and available in a normal NHL game, however, is 20.