Third-party carrier-calculated shipping
You can connect your own account with carriers such as UPS, FedEx, USPS, Canada Post, or Australia Post to display real-time shipping rates at checkout. When customers check out, Shopify requests live rates from your connected carrier accounts based on the order's weight, dimensions, and destination, then displays those rates as shipping options. This ensures customers pay the exact amount your carrier will charge you for the shipping label.
When your products have a packed product size, the items in each shipment are packed into the smallest of your saved boxes that fits them. The rates are then estimated for each shipment's box instead of your store default package.