I prefer my veggie burgers to be moderate in size: about 4 inches (10 cm) in diameter and ¾ inch (2 cm) thick. If you shape the burgers any larger, they become difficult to eat with a bun, and you run the risk of having them fall apart when you flip them. If they’re any smaller, they’ll seem like an afterthought to the hamburger bun. That said, if you’re not serving your burgers on buns, then you have much more flexibility.
Veggie burger “sliders” are also a fun variation. Simply shape rounded tablespoons of the mixture into small patties and then sauté. See note below regarding cooking time and cooking method.