What is the usual length of treatment with antibiotics?

Depends on abx, infx. Some antibiotic treatments for certain infections may be a single one-time dose, while others may need to be continued for weeks or even months. The decision of which antibiotic to use and for how long to treat depends on the type of infection, what part of the body is infected, and the health of the person who has the infection. Post a more specific question for more detailed answer.