How many mb is an android free app?

I don't think you need an app. I think you just go to settings and check storage space (measured in GB or KB) 

... https://play.google.com/store/apps/details?id=com.radioopt.widget ... https://play.google.com/store/apps/details?id=com.netqin.mobileguard ... .google.com/store/apps/details?id=com.onavo.android.onavoid&hl=en