Cacher is the code snippet organizer for pro developers

<?php
/**
 * WooCommerce Extra Feature
 * --------------------------
 *
 * Change number of related products on product page
 * Set your own value for 'posts_per_page'
 *
 */ 
function woo_related_products_limit() {
  $args = array(
    'post_type'			=> 'product',
    'no_found_rows' 		=> 1,
    'posts_per_page' 		=> 6
  );
  return $args;
}
add_filter( 'woocommerce_related_products_args', 'woo_related_products_limit' );