You can specify a particular row in your spreadsheet to be used as the bar width for your chart.
1.Click on the Bars/Series button in the Edit Chart Toolbar
2.Click on the Bars and Series Task Pane
3.The Widths drop down menu contains all the spreadsheet rows in your chart. You can create and select a specific row from the spreadsheet to set the bar widths. Alternatively, the width can be set to automatic.
You may also set a bar as the bar width directly in the datasheet. Simply right click on the desired bar column header and from the Show Bar drop down menu in the floating toolbar, select Bar as Width.