What miracles do you need to do to become a saint?

Miracles were not required for declaring a person a saint in the early years of Christianity. The person would have been declared a saint by popular acclamation to a bishop based on the lives and merits of the candidate. This was especially true if the person died the death of a martyr as it was felt that making this ultimate sacrifice for Our Lord would be an automatic designation of that person as a saint.

Even today, miracles are not always a requirement for canonization, especially in the case of martyrs.

Today the Church usually requires at least one miracle be proven for beatification and another for canonization. The miracle that is proven must have occurred because of the intercession of the candidate for sainthood and must be shown by scientist and doctors to be beyond a doubt a true event that defies all explanation.