USPS Flate Rate Shipping - Boxes

We are running CS Cart MV. 2.2.

For shipping options in our store, we are looking to begin with only USPS and basic shipping services, and potentially expand after we start getting some sales traction.

We want to USPS Flat Rate boxes, Small/Med/Large, as this is the most cost effective way (imo) to ship with USPS. We are only shipping within the US.

Ideally, we want CS Cart to determine based on weight and/or “Items in a box” to be used in conjunction to determine the optimal boxe(s) to use for shipping. So essentially the software’s logic should be able to take a look at the items being purchased and determine whether they can be used in a small, med, or large box - and if there are many items, determine what combination is best.

Currently - it seems like CS Cart, stock, can only use perhaps one flat rate box or another, not a combination of different sizes. Perhaps I’m wrong.

Anyone have any thoughts on this? I’ve been thinking/searching for some time but cannot wrap my head fully around how it may work.



Any ideas on Flat Rate Boxes options? Currently we are proceeding with simply only providing Priority mail, but any help would be appreciated.


Just went through the same process. Since FR boxes can weigh up to 70 LBS, regardless of the size of the box, the only way to solve this is to setup a manual shipping rates. We have a tshirt shop who wants to ship with USPS FR boxes but, they don't weigh much therefore, we setup shipping based on quantity vs weight. Use the shipping rules to get creative.