PayPal offers quite a few robust options for calculating shipping within your PayPal account. One of those options is to base the shipping on the total weight of the order.
It would be really nice if Gravity Forms offered some way to associate a weight (in lbs. or kg.) with each product on the form, total up that weight based on the quantity of each product added, then send that as the
weight parameter to PayPal (along with the
weight_unit parameter). Thanks.