Please help to understand Orthographic camera size

Orthograp$$anonymous$$c size means how many units in world space the viewport half height is. So when you set Orthograp$$anonymous$$c size to 5.8, it simply means that for example a cube placed at coordinates (0f, 5.8f) has it's pivot point aligned with the top of the screen (bottom half of it should be visible because the pivot is in the middle by default)

The camera will always show that same amount of world units on the screen height-wise regardless of resolution. So if you look at the game on a 200x100 pixel screen, Unity will try to render exactly the same part of the game world on the screen with a 400x200 screen. The picture will just be more detailed because the device has a better resolution.

Depending on the device's screen aspect ratio, the visible world area WIDTH can change and can be calculated based on the orthograp$$anonymous$$c size and device resolution

   float screenHeightInUnits = Camera.main.orthograp$$anonymous$$cSize * 2;
   float screenWidthInUnits = screenHeightInUnits * Screen.width/ Screen.height; // basically height * screen aspect ratio