Rule 108.2

When a rule or text on a card refers to a “card,” it means only a Magic card. Most Magic games use only traditional Magic cards, which measure approximately 2.5 inches (6.3 cm) by 3.5 inches (8.8 cm). Certain formats also use nontraditional Magic cards, oversized cards that may have different backs. Tokens aren’t considered cards—even a card that represents a token isn’t considered a card for rules purposes.

Find this number in the current Rules