add auto number in Gridview

<asp:GridView ID="GridView1" runat="server" AllowPaging="True" AutoGenerateColumns="False"
DataSourceID="SqlDataSource1" PageSize="6" AlternatingRowStyle-BackColor="#006699"
AlternatingRowStyle-ForeColor="#FFFFFF">
<Columns>
<asp:TemplateField HeaderText="Serial Number">
<ItemTemplate>
<%# Container.DataItemIndex + 1 %>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name" />
<asp:BoundField DataField="Location" HeaderText="Location" SortExpression="Location" />
</Columns>
</asp:GridView>
 
Reference