What are the legal requirements for making business cards?

There are typically no legal requirements except for that you must provide true and correct information on the card and be the person represented. In terms of size, standard size is 2 inches by 3.5 inches (so that it fits into wallets and most card holders) however many non-conventional designers will push these restrictions to make a statement when designing business cards. You should check with the printer before designing them yourself for further requirements.