This little snippet works when you have an array of packages and you want to get the weight of individual packages in WooCommerce. Usually used in the calculate shipping method. http://docs.woothemes.com/document/shipping-method-api/

wc-get-products-weight.php

<?php
foreach ( $package['contents'] as $item_id => $values ) {
	// skip products that dont need shipping
	if ( $values['data']->needs_shipping() ) {
		// make sure a weight is set
		if ( $values['data']->get_weight() ) {
			$item_weight = $values['data']->get_weight();

			// do something with the weight here
			// ...
		}
	}
}