Decimal summ = 0;
for (int n = 0; n < Cusinvoicegrid0.Rows.Count; ++n)
{
summ += Convert.ToDecimal(Cusinvoicegrid0.Rows[n].Cells[3].Text);
}
summ =Convert.ToDecimal(summ.ToString("#,##0.00;-$#,##0.00;0.0"));
Label3.Text = summ;
let me know it works r not