USPS Shipping Method for WooCommerce

In my old ecommerce store, I used other software but for the USPS addon, we had a nice feature that we added the actual weight of the product to the product, but we could add a percentage weight or just a normal weight (say the weight of a box) so during the calculation of weight, it would take into account the weights of the product and include the weight of the shipping box. For example, I have many products that weigh next to nothing, I could add ten of them and still only weigh ounces. But when I add a box, it doubles or triples the weight for calculation so I lose money sometimes when I ship products.