Shipping a product where the variants are different weights, shipping label accurate?

[ScottTArmstrong]

I sell product by the pound. The way I set up the products to sell by quantity is by inputting the popular sold volumes as variants. The options for each product is to purchase them in 10, 20, 30, 40, and 50lbs increments. My question is how do I make sure the shopify shipping label reflects the correct weight? Is there an option for it to automatically update the label or do I need to manually input it? Also, the max I will ship in one box is 50lbs. So if someone orders say 100lbs, is there a way for me to print off two shipping labels for one order?