Hi Waghmare,

Just assign the ItemStyle-Width like ItemStyle-Width="100px" to set the BoundField or TemplateField.

HTML

<asp:GridView ID="GVDetails" runat="server"   AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Description" ItemStyle-Width="100px" HeaderText="Description" />
        <asp:TemplateField ItemStyle-Width="100px"  HeaderText="Description">
            <ItemTemplate>
                <asp:Label ID="lblDescription" runat="server" Text='<%#Eval("Description") %>'>                       
                </asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Screenshot