What is the average game file size for a windows Standalone?
I don’t think there is an average file size. It all depends on the scope of the game. The size of my game reached 35MB recently, but it was much smaller in the beginning, and I am sure it will grow quite a bit until I am finished, as I will be adding more assets and levels.
90%+ of the file size is just regular models, textures and sounds. The parts you add in Unity – scripts, prefabs, gameObjects, scenes … – aren’t very big. If you have a 20 Meg pile of Assets, you’ll probably have a 21 Meg game.
Unity Terrain is the one exception. Each can chew up a few Megs (browse to the folder, to see.) It might be worth figuring out how to lower the settings (HT map, splat map) to save space.