The size of a Christmas card can vary depending on the intended recipient. For example, if you're sending a Christmas card to a family, you might want to use a larger size card that can accommodate multiple signatures or messages. On the other hand, if you're sending a card to a single individual, a smaller card may be more appropriate. Ultimately, the size of a Christmas card is a matter of personal preference and should be chosen based on who you're sending it to and what you want to say.