When the spreadsheet is set to the size of the viewable range and you turn automatic sizing on, the spreadsheet expands and shrinks on the Web page depending on content. It changes size as necessary when you insert and delete rows and columns, or when you change row heights or column widths.
If you want to prevent the spreadsheet from expanding beyond a specified size, type a value — either in pixels or as a percentage of the entire Web page — in the Max height box or the Max width box, or in both boxes. For example, to allow the spreadsheet to expand up to half the width of the Web page, type 50% in the Max width box. To limit the width of the spreadsheet to 300 pixels, type 300 in the Max width box.