Insert a custom total row on cart and checkout tot

In woocommerce, I have successfully managed to add a custom field to a Woocommerce simple product and display that value on the additional info tab on a product page.

Now I am totally lost with the final piece of my jigsaw trying to insert a total row in cart and checkout pages with for the total calculated volume.

The custom field is to store the volume in m3 of a furniture item. When a client adds an item to the basket I would like to calculate the total m3 of the shipment by adding the values of all the custom fields together and displaying the total to the customer on the page. Can anyone point me in the right direction of how to add these custom fields and display them please.

So far my code looks like this

    // Display Fields using WooCommerce Action Hook
add_action( 'woocommerce_product_options_general_product_data', 'woocom_general_product_data_custom_field' );

function woocom_general_product_data_custom_field() {
  // Create a custom text field


  // Number Field
  woocommerce_wp_text_input( 
    array( 
      'id' => '_item_volume', 
      'label' => __( 'Item Shipping Volume', 'woocommerce' ), 
      'placeholder' => '', 
      'description' => __( 'Enter the volume her in m3.', 'woocommerce' ),
      'type' => 'number', 
      'custom_attributes' => array(
         'step' => 'any',
         'min' => '0.001'
      ) 
    )
  );

}

// Hook to save the data value from the custom fields
add_action( 'woocommerce_process_product_meta', 'woocom_save_general_proddata_custom_field' );

/** Hook callback function to save custom fields information */
function woocom_save_general_proddata_custom_field( $post_id ) {

  // Save Number Field
  $number_field = $_POST['_item_volume'];
  if( ! empty( $number_field ) ) {
     update_post_meta( $post_id, '_item_volume', esc_attr( $number_field ) );
  }

}

add_action( 'woocommerce_product_additional_information', 'custom_data_in_product_add_info_tab', 20, 1 );
function custom_data_in_product_add_info_tab( $product ) {

    //Product ID - WooCommerce compatibility
    $product_id = method_exists( $product, 'get_id' ) ? $product->get_id() : $product->id;

    // Get your custom fields data
    $custom_field1 = get_post_meta( $product_id, '_item_volume', true );


    // Set your custom fields labels (or names)
    $label1 = __( 'Shipping Volume m3', 'woocommerce');


    // The Output
    echo '<h3>'. __('Item Shipping Volume', 'woocommerce') .'</h3>
    <table class="custom-fields-data">
        <tbody>
            <tr class="custom-field1">
                <th>'. $label1 .'</th>
                <td>'. $custom_field1 .'</td>
            </tr>
        </tbody>
    </table>';
}

The following will display the total cart volume in cart and checkout page:

add_action( 'woocommerce_cart_totals_before_shipping', 'display_cart_volume_total', 20 );
add_action( 'woocommerce_review_order_before_shipping', 'display_cart_volume_total', 20 );
function display_cart_volume_total() {
    $total_volume = 0;

    // Loop through cart items and calculate total volume
    foreach( WC()->cart->get_cart() as $cart_item ){
        $product_volume = (float) get_post_meta( $cart_item['product_id'], '_item_volume', true );
        $total_volume  += $product_volume * $cart_item['quantity'];
    }

    if( $total_volume > 0 ){

        // The Output
        echo ' <tr class="cart-total-volume">
            <th>' . __( "Total Shipping Volume", "woocommerce" ) . '</th>
            <td data-title="total-volume">' . number_format($total_volume, 2) . ' m3</td>
        </tr>';
    }
}

Code goes in function.php file of your active child theme (or active theme). Tested and works.