I’ve made a proyect with nothing in it. No scripts,gameobjects or folders, just the main camera and the directional light. When i build the project it is saved as 17.73 MB but if i installed it on my mobile it grows to 35.15 MB. Why does it happen?
Have you deployed to Apple or Android??.If android, when you create an apk the apk size will be above 16mb as it supports both ARM v7 and x86 devices if you want your apk to support only ARM v7 devices ,change device filter to ARM v7 then your apk size would be around 8 to 12 mb.
You can change the device filter setting under player settings->configuration->device filter.
most of the android devices are ARM v7 ,considerably very few devices supports Intel’s X86.
Have a look on this link which gives you some idea about ARM v7 and X86