This function tells you how many bytes a folder, with all subfolders and contained files is taking on a HD, CD, floppy or whatever.

I'll put here just the code... that isn't very
complicated:

function FolderSize(fld: string):dword;
var
  sr:tsearchrec;
  r:integer;
  s:dword;
begin
  fld:=includetrailingbackslash(fld);
  s:=0;
  r:=findfirst((fld+'*.*'),faanyfile,sr);
  while(r=0)do
  begin
    application.processmessages;
    if((sr.attr and fadirectory)<>0)then
    begin
      if((sr.name<>'.')and(sr.name<>'..'))then
        s:=s+foldersize(fld+sr.name);
    end else
      S:=S+SR.FindData.nFileSizeLow;
    r:=findnext(sr);
  end;
  sysutils.findclose(sr);
  result:=s;
end;