Display upload file size in kb in collection list view

I am trying to display the file size for my media collection in kb. I tried adding a function to transform the bytes that

returns to kb, but

only allows for strings and I am not sure where to access the raw filesize data itself to transform.

  defaultColumns: ['filename', 'alt', 'width', 'height', 'filesize' ]

Is there any way to display this in the collection list view? I see the file size displayed as kb in the individual media view, but can't find where to access that for

.