We have product of various sizes/weights. Is Shopify able to recognize that multiple, dissimilar items can fit in a single USPS flat rate box, know how many of said different products ( ie: how many widgets AND corkscrews combined ) will fit in a single USPS flat rate box, and recognize when one USPS flat rate box would be at capacity and another is required?
From all my reading about shipping, it seems the answer is "No, not without an additional App" but I want to pick others brains before resigning myself to that end.
I'm Miles from the Social Care team at Shopify. Welcome to the community!
I just wanted to reply to this post to let you know that the built-in Shopify settings for shipping don't currently allow for the customizations you're after. I just wanted you to hear this from Shopify directly so you know you aren't being led astray by others.
Shopify tries to make e-commerce as easy and accessible for everyone from beginners to experts. To do this, the Shopify admin is designed so there are enough features to build a workable store, without being too complex or complicated. To achieve this, the Shopify App Store was created for developers to work solutions for merchants who need customizations outside of what's already built.
With that, I've made an app suggestion below for you. If it's not suitable, be sure to check out other shipping apps too.
I hope this has helped to clarify your concerns, but please let me know if you have any questions at all.