Font family, size, etc. depends on "Graphics" style in the notebook stylesheet

CurrentValue[{StyleDefinitions, "Graphics", "FontSize"}]
 (* 10 *)

CurrentValue[{StyleDefinitions, "Graphics", "FontFamily"}]
 (* "Times" *)

You can manually change it: open Format->Edit Stylesheet..., add

 Cell[StyleData["Graphics"],FontSize->20]

and press Ctrl+Shift+E. You will see that the font in Plot,LinePlot, etc. instantly increase.

Font family, size, etc. depends on "Graphics" style in the notebook stylesheet

CurrentValue[{StyleDefinitions, "Graphics", "FontSize"}]
 (* 10 *)

CurrentValue[{StyleDefinitions, "Graphics", "FontFamily"}]
 (* "Times" *)

You can manually change it: open Format->Edit Stylesheet..., add

 Cell[StyleData["Graphics"],FontSize->20]

and press Ctrl+Shift+E. You will see that the font in Plot,LinePlot, etc. instantly increase.

Edit: default values for Plot, ListPlot, etc. separately can be set by

SetOptions[Plot, BaseStyle -> {FontFamily -> "Helvetica", FontSize -> 16}]

Font family, size etc. depends on "Graphics" style in the notebook stylesheet

CurrentValue[{StyleDefinitions, "Graphics", "FontSize"}]
 (* 10 *)

CurrentValue[{StyleDefinitions, "Graphics", "FontFamily"}]
 (* "Times" *)

You can manually change it: open Format->Edit Stylesheet..., add

 Cell[StyleData["Graphics"],FontSize->20]

and press Ctrl+Shift+E. You will see that the font in Plot,LinePlot, etc. instantly increase.

Font family, size, etc. depends on "Graphics" style in the notebook stylesheet

CurrentValue[{StyleDefinitions, "Graphics", "FontSize"}]
 (* 10 *)

CurrentValue[{StyleDefinitions, "Graphics", "FontFamily"}]
 (* "Times" *)

You can manually change it: open Format->Edit Stylesheet..., add

 Cell[StyleData["Graphics"],FontSize->20]

and press Ctrl+Shift+E. You will see that the font in Plot,LinePlot, etc. instantly increase.