Boxify’s determination of shipping rates is not affected by what you have set for your Shopify “packages” on the Settings > Shipping and delivery page of your shop. Boxify uses the boxes you have configured in the app for that. Your Shopify packages are, however, relevant if you are using Shopify’s built-in tools during fulfillment to purchase shipping labels. Boxify is not involved in the purchase of shipping labels, so you’ll need to purchase a shipping label for the appropriate Shopify package.

When you go to fulfill an order and purchase a shipping label for it with Shopify, the package shown at the outset will be whichever one you designated as your default package in Shopify. When you go to purchase a shipping label, Shopify doesn’t know at the outset which package is appropriate to use for shipping the order. Nor is it technically possible for Boxify to control the choice of package to purchase the label for: this part of the Shopify platform is not open to apps. You’ll have to select the appropriate Shopify package manually.

So if you are using Shopify’s built-in tools to purchase shipping labels, you should set up Shopify packages that match the boxes you have configured in Boxify. But take care about what dimensions you use to define those Shopify packages: don’t just copy the box dimensions you used to configure boxes in Boxify. When you configure boxes in Boxify, you enter their interior dimensions. Those are important to define exactly because they determine what can be packed inside. But what the carriers care about when the price a shipment, of course, are the exterior dimensions of the box.

Before getting shipping rates from the carriers, Boxify estimates exterior dimensions of shipping boxes by adding 7 mm all around to the interior dimensions set to account for the thickness of even beefy box cardboard. This adds a little over 1/2 inch to each interior dimension. Shopify, on the other hand, doesn’t make any such adjustment and simply asks you to enter the exterior dimensions when you configure your Shopify packages.