function ByteToMegaByte(Byte: Integer): Integer;
begin
result := Byte div 1024 div 1024;
end;

public string SizeString
{
    get
    {
        float size = FileSize;
        int divs = 0;

        while (size > 1024)
        {
            size /= 1024;
            divs++;
        }

        string unit;
        switch (divs)
        {
            case 0: unit = " Byte"; break;
            case 1: unit = " KB"; break;
            case 2: unit = " MB"; break;
            case 3: unit = " GB"; break;
            default: unit = ""; break;
        }

        return (string.Format("{0:F2}",size) + unit);
    }
}

function FileSizeToString(const FileSize: Int64): String;
const Measure: Array[0..4] of String = ('Byte', 'KB', 'MB', 'GB', 'TB');
var NewSize: Currency;
var i: Integer;
begin
  Result := '';

  if FileSize > -1 then
  begin
    i := 0;
    NewSize := FileSize;

    while (NewSize >= 1024) do
    begin
      NewSize := NewSize / 1024;
      Inc(i);
    end;

    case i of
      0: Result := FloatToStr( NewSize );
      1,
      2,
      3: Result := FormatFloat('0.00', NewSize);
      4: Result := FormatFloat('0.000', NewSize);
    else Result := FloatToStr( NewSize );
    end;

    Result := Result + #32 + Measure[i];
  end;
end;

Function SizeToString(Size: LargeInt): String;
    Var i: LargeInt;

    Begin
      i := Abs(Size);
      If i < 1000 Then Result := Format('%.0n B', [Size / 1])
      Else If i < 10235 Then Result := Format('%.2n KB', [Size / 1024])
      Else If i < 102349 Then Result := Format('%.1n KB', [Size / 1024])
      Else If i < 1023488 Then Result := Format('%.0n KB', [Size / 1024])
      Else If i < 10480518 Then Result := Format('%.2n MB', [Size / 1048576])
      Else If i < 104805172 Then Result := Format('%.1n MB', [Size / 1048576])
      Else If i < 1048051712 Then Result := Format('%.0n MB', [Size / 1048576])
      Else If i < 10732049531 Then Result := Format('%.2n GB', [Size / 1073741824])
      Else If i < 107320495309 Then Result := Format('%.1n GB', [Size / 1073741824])
      Else If i < 1073204953088 Then Result := Format('%.0n GB', [Size / 1073741824])
      Else If i < 10989618719622 Then Result := Format('%.2n TB', [Size / 1099511627776])
      Else If i < 109896187196212 Then Result := Format('%.1n TB', [Size / 1099511627776])
      Else If i < 1098961871962112 Then Result := Format('%.0n TB', [Size / 1099511627776])
      Else If i < 11253369568892027 Then Result := Format('%.2n PB', [Size / 1125899906842624])
      Else If i < 112533695688920269 Then Result := Format('%.1n PB', [Size / 1125899906842624])
      Else If i < 1125336956889202688 Then Result := Format('%.0n PB', [Size / 1125899906842624])
      Else Result := Format('%.2n EB', [Size / 1152921504606846976]);
    End;