Input String was not in correct Format

Dear All,

Based on below code, May i know how to convert the data ? For the UnitCost  input Data is float.

Kindly advise, thank you

  protected void CalNett_TextChanged(object sender, EventArgs e)
        {

            int GrossWeight = Convert.ToInt32(WMGrossWeight.Text.ToString());
            int UnitCost = Convert.ToInt32(WMUnitCost.Text.ToString());

    


            decimal NettWeight = (GrossWeight - 85);
            decimal TotalCost = (NettWeight * UnitCost);



            if (WMItem.SelectedValue == "SW.307.004 ")

                this.WMTotalCost.Text = TotalCost.ToString();

            }