File size limit for a document in SharePoint is actual file size or file size on disk

Question

The file size upload limit for a document is 50mb by default but is it file size of the document or file size of document on disk.

Answer 1

After comparing disk space, to site collection (Adding removing a site collection) The quota is based on the actual file sizes.

To get the site collection totals:

$site = Get-SPSite http://sitecollection
$site.Usage.Storage;
$site.Dispose();

Answer 2

There's isn't any big difference at all as said by Hossein Aarabi but limit is for file size not file size on disk as far as I find out by research however couldn't find any reference.