use
ItemStyle-Width property in design time, see below:
Code:
<asp:DataGrid id="myDataGrid" AutoGenerateColumns="False" Runat="Server">
<Columns>
<asp:BoundColumn HeaderText="Product Name" DataField="ProductName" ItemStyle-Width="333" />
</Columns>
</asp:DataGrid>
HTH.
Always:),
Hovik Melkomian.