Bytes to file size

Problem/Question/Abstract:

How I can convert bytes to file size in KB/MB like in windows explorer

Answer:

function FileSizeStr(Size: LongInt): string;
begin
  if Size < 1000 then
    Result := IntToStr(Size) + ' B'
  else if Size < 102400 then
    Result := IntToStr((Size + 1023) shr 10) + ' KB'
  else
    Result := IntToStr((Size + 1048575) shr 20) + ' MB';
end;