How to know the right size for android

Hi everyone, I am creating a game for android, already created the widgets of the menus and the game is programmed in the blueprint of the level … my doubt is about the right size of the canvas for android … in the widget you can choose the mobile models which shows beside its size … but at the level I did not find anything to change the size according to some model of smartphone … can anyone help me? thank you so much!