Limited decks must contain a minimum of forty cards. There is no maximum deck size.
Any drafted or opened
cards not used in a player’s Limited deck function as their sideboard. Players are not restricted to four of any one card in Limited tournament play.
One of the most frequent questions by newer players is if they are allowed to play more than four copies of a card in limited. The answer is yes! Note that they can of course play the cards in their main, or are allowed to have excess copies in their sideboard. A good idea is to have players who have more than four of particularly good cards mention it to you ahead of time. This can help offset any potential accusations of cheating.