Add shipping surcharge based on specific equation

shipping-surcharge-calculated-dimensions.php

/**
 * Add surcharge for every item where this dimensions equation exceeds 3m
 * Code snippets should be added to the functions.php file of your child theme
 *
 * @return array
 */
function add_surcharge_for_large_items( $rates, $package ) {
    // information used in calculations that can be edited
    $shipping_method = 'betrs_shipping;
    $fee = 4.99;
    $max_dimensions = 3;
    $total_width = $highest_length = $highest_height = 0;
 
    // determine calculated dimensions for entire order
    foreach( $package['contents'] as $key => $values ) {
        $cart_data = $values['data'];
        
        // combine all widths
        $total_width += $cart_data->get_width();
        
        // find largest length
        if( $cart_data->get_length() > $highest_length )
            $highest_length = $cart_data->get_length();
            
        // find largest height
        if( $cart_data->get_height() > $highest_height )
            $highest_height = $cart_data->get_height();
    }
    $calc = floatval( $highest_length ) + floatval( $total_width * 2 ) + floatval( $highest_height * 2 );
    if( $calc >= $max_dimensions )
        $extra_fee = $fee * $large_items;
 
    // add fee to all options from method specified above
    foreach( $rates as $key => $rate ) {
        if( $rate->method_id != $shipping_method )
          continue;

        $rates[ $key ]->cost += $extra_fee;
    }
 
    return $rates;
}
add_filter( 'woocommerce_package_rates', 'add_surcharge_for_large_items', 10, 2 );