DataGridView Multiplicating Two Columns

I'm in need of the community's help. I am trying to multiply the values of two columns in a DataGridView (WPF and C#), the first column get its data from a MySql database and the second column is an input value where a user will type a number which should be multiplied with the first column and the result should be displayed in a third column called "Total". I have searched all over and tried different approaches from other people who tried the nearly same thing but I just can't get the value to multiply and the result to appear in the third column. Here's the last bit of code I've tried, I have to mention that I am still very new to C# and WPF with not so much experience:

<DataGrid AutoGenerateColumns="False" x:Name="tblData" Margin="30,197,7,0" Grid.Row="1" VerticalAlignment="Top" Height="510" Grid.ColumnSpan="4"
              BorderThickness="2" BorderBrush="#FF445BBF" ItemsSource="{Binding Path=LoadDataBinding}" CanUserResizeRows="False" ClipToBounds="True"
              CanUserSortColumns="False" HorizontalGridLinesBrush="#FFC7C7C7" VerticalGridLinesBrush="#FFC7C7C7" IsManipulationEnabled="True" EnableRowVirtualization="False" 
              IsTextSearchEnabled="True" xmlns:local="clr-namespace:PoS_Pimentel">
        <DataGrid.Resources>
            <local:AmmountConverter x:Key="AmmountConverter" />
        </DataGrid.Resources>
        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding Path=nomprod}" Header="Producto" Width="500" IsReadOnly="True">
                <DataGridTextColumn.HeaderStyle>
                    <Style TargetType="DataGridColumnHeader">
                        <Setter Property="HorizontalContentAlignment" Value="Center" />
                        <Setter Property="FontSize" Value="14" />
                    </Style>
                </DataGridTextColumn.HeaderStyle>
            </DataGridTextColumn>
            <DataGridTextColumn Binding="{Binding Path=preciogram, Mode=TwoWay}" Header="Precio por Gramo" Width="190" IsReadOnly="True">
                <DataGridTextColumn.HeaderStyle>
                    <Style TargetType="DataGridColumnHeader">
                        <Setter Property="HorizontalContentAlignment" Value="Center" />
                        <Setter Property="FontSize" Value="14" />
                    </Style>
                </DataGridTextColumn.HeaderStyle>
            </DataGridTextColumn>
            <DataGridTextColumn Binding="{Binding Path=gramos, Mode=TwoWay}" Header="Gramos" Width="190" IsReadOnly="False">
                <DataGridTextColumn.HeaderStyle>
                    <Style TargetType="DataGridColumnHeader">
                        <Setter Property="HorizontalContentAlignment" Value="Center" />
                        <Setter Property="FontSize" Value="14" />
                    </Style>
                </DataGridTextColumn.HeaderStyle>
            </DataGridTextColumn>
            <DataGridTextColumn Binding="{Binding Path=total, Mode=TwoWay}" Header="Total" Width="*" IsReadOnly="True">
                <DataGridTextColumn.HeaderStyle>
                    <Style TargetType="DataGridColumnHeader">
                        <Setter Property="HorizontalContentAlignment" Value="Center" />
                        <Setter Property="FontSize" Value="14" />
                    </Style>
                </DataGridTextColumn.HeaderStyle>
            </DataGridTextColumn>
        </DataGrid.Columns>
    </DataGrid>

and on the C# end I created two separate .cs file for an EntitiyClass and an AmmountConverter class:

EntityClass code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.ComponentModel;
using System.Collections.ObjectModel;
using System.Windows.Forms;

namespace PoS
{
    #region
    public class Entity_Class : INotifyPropertyChanged
    {
        private int _preciogram;
        public int PrecioGram
        {
            get { return _preciogram; }
            set { _preciogram = value; NotifyPropertyChanged("gramos"); }
        }

        private int _gramos;
        public int Gramos
        {
            get { return _gramos; }
            set { _gramos = value; NotifyPropertyChanged("gramos"); }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void NotifyPropertyChanged(string propertyName)
        {
            if(PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}

And the AmmountConverter class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Data;

namespace PoS_Pimentel
{
    public class AmmountConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            double prcgrms = values[1] == null ? 0 : System.Convert.ToDouble(values[1]);
            double grms = values[2] == null ? 0 : System.Convert.ToDouble(values[2]);

            return prcgrms * grms;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

I'm not very good at this but I am trying and any pointers will be greatly appreciated. Thank you all.