I am selling a set of coffee mugs that is shipped in a single box. My account is set up to auto-calculate shipping charges using the Shopify UPS discounts. Shipping one box costs about $13 to ship via UPS. If a customer purchases two boxes the shipping cost should be $26 because I need to send the shipment in two separate boxes with two labels, but instead Shopify charges the customer about $15.50. Does anyone know how I can set up my account so that the shipping charge is correct?
You're experiencing this because Shopify only sends off one box size for live rate calculations called your 'default box size'. You'll need a third-party app like Smart Boxing to have access to accurate live rates and unlimited box sizes.
The only caveat is that Shopify doesn't give third-party apps access to their negotiated rates. You can add a discount within the app to mimic these, or as a lot of our users do, they pocket the difference and use it for incidentals such as lost packages, chargebacks and other order disputes. It also gives you an extra buffer to add in fun things like candy and custom notes printed on beautiful card stock, or to level up your packaging.
Another option if you don't want to use an app solve your problem is charging flat rates and using Shopify's shipping profiles. You could create a profile for mugs, for example, and set it for the weight of one set it's $13, but for two sets it's $26. The problem with Shopify's shipping profiles, however, is that the moment you add in "rules", the end shipping cost your customers get can be very wrong. This is because Shopify bases the final shipping cost on the cart total.
Let's say you had a setup like this:
Mug sets weigh 4 lbs each and are set for $13 for every 4lbs.
Vases each weigh 6 lbs and are set for $18 for every 6 lbs.
Everything else in the store is a flat $10 for shipping.
If a customer ordered 1 set of mugs, 1 vase, and a 4lb item from the General Shipping Profile. they would be charged $72 for shipping. This is because the cart weight of 14 lbs triggers the maximum charge from each profile. Their system doesn't do each item/profile separately. In a perfect world (or the world of Intuitive Shipping), they would combine together at checkout however you need them to.
I hope this helps!