How to calculate Total price on textbox change event in Gridview.

Step 1 : Apply JavaScript code under a <head > tag.

 <script type="text/javascript">
 function CalcSellPrice2(CurrentPrice, QuntValue, TotalValue) {
var QuntVar = parseFloat(document.getElementById(QuntValue).value);
var TotalVar = document.getElementById(TotalValue);
var TotalPriceValue = parseFloat(CurrentPrice * QuntVar);
TotalVar.innerHTML = TotalPriceValue;
}
 </script>

Step 2 : Grid View Source Code.

 <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnRowDataBound="GridView1_RowDataBound">
 <Columns>
 <asp:TemplateField HeaderText="List Price" Visible="True">
 <ItemTemplate>
 <asp:Label ID="lblCurrentListPrice" runat="server" Text='<%# Eval("Price") %>'></asp:Label>
 </ItemTemplate>
 </asp:TemplateField>
 <asp:TemplateField HeaderText="Qunt">
 <ItemTemplate>
 <asp:TextBox ID="txtqut" Width="100px" runat="Server" />
 </ItemTemplate>
 </asp:TemplateField>
 <asp:TemplateField HeaderText="Total Price">
 <ItemTemplate>
 <asp:Label ID="lblTotal" runat="Server" />
 </ItemTemplate>
 </asp:TemplateField>
 </Columns>
 </asp:GridView>

Step 3 : Apply code on page.cs part.

 using System;
 using System.Data;
 using System.Configuration;
 using System.Collections;
 using System.Web;
 using System.Web.Security;|
 using System.Web.UI;
 using System.Web.UI.WebControls;
 using System.Web.UI.WebControls.WebParts;
 using System.Web.UI.HtmlControls;
protected void Page_Load(object sender, EventArgs e)
{
GridView1.DataSource = GetData();
GridView1.DataBind();
}
public DataSet GetData()
{
DataSet ds = new DataSet();
DataTable dt = new DataTable("Product");
DataRow dr;
dt.Columns.Add(new DataColumn("Price", typeof(Int32)));
dt.Columns.Add(new DataColumn("Qut", typeof(Int32)));
dt.Columns.Add(new DataColumn("TotalPrice", typeof(Int32)));
for (int i = 1; i <= 10; i++)
{
dr = dt.NewRow();
dr[0] = (20 * i);
dt.Rows.Add(dr);
}
ds.Tables.Add(dt);
Session["dt"] = dt;
return ds;
}
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
Label lblCurrentListPrice = (Label)e.Row.FindControl("lblCurrentListPrice");
Double CurPr = Convert.ToDouble(lblCurrentListPrice.Text);
TextBox txtqut = (TextBox)e.Row.FindControl("txtqut");
Label lblTotal = (Label)e.Row.FindControl("lblTotal");
txtqut.Attributes.Add("onkeyup", "CalcSellPrice2(" + CurPr + ", '" + txtqut.ClientID + "','" + lblTotal.ClientID + "')");
}
}

Step 4 : Run page and getting out put thanks.