Google Photos, media file size

Question

I am using the Google Photos API and want to find a way to check how much of a user's online storage space a given media item occupies. To be clear, this is potentially different from the actual file size of the image / video. Images in shared albums might occupy a different user's storge, or media uploaded before a certain date or from an OG pixel might not occupy any of the user's storage space. If I can't check the actual storage used, checking whether or not it occupies any storage space would also be useful, as would a way to search for media based on this.

Does anyone know if / how this can be done?

Thanks in advance!