Please help —No “Large” Option Listed for USPS Flate Rate Box?

New Member
2 0 5

Hi there Shopify forums!

I have a large flat rate box I am trying to ship out ASAP. For some reason there is no option for this size, all other sizes are available but this one?

It’s very strange— I find the size, flat rate large 12 x 12 x 5.5, but it is available only for APO Army Adresses, I don’t think I should select this though for fear it will be returned back to me?

Should I go ahead and list under custom box ( even though this is a USPS flate rate?)  


I regularly use this box size for my large items and could possibly go through USPS shipping but I would love to go through this Platform as I keep many tracking numbers stored here and wouldn’t want them separated using outsourced shipping. Wondering if there’s any way we can add this box size into the shipping category. 


Any and all help is appreciated

Replies 17 (17)
7 0 13
In the past, it wasn't there for me either, but when I went back a few days ago, it was there.  I don't know why it's not showing up for you.  This is definitely a question for the Shopify help center.
New Member
1 0 0

So read the forum and it is not popping up for me either.  I went to the USPS site and it was going to cost me $22.10 to ship it from there.  I had an idea and cut the glued flap from the inside of my flat rate box and turned the box inside out and taped the flap back into position.  Now, none of the "Flat Rate Box" writing is visible and it looks pretty much like a standard box with some writing regarding Priority Mail Service.  That same box cost me $9.60 to ship from Shopify.  I will let you know if I get kick back out of it, but I don't really see why I would. 



5 0 2

Thank you, but this is exactly what I tried, and the Large Flat Rate Box option is not listed.  Perhaps it is only for some customers...

5 0 2

Never mind! You are 100% correct! This is a great solution. Thank you!!!

New Member
1 0 0

Solved! I had the same issue. I was able to go to Settings > Shipping and Delivery > Packages > Add Package. I was able to add it there and when I went back to my order it showed up as an option in my saved packages. 

Good luck!

New Member
2 0 1

Same here, it is not there under add package. What gives shopify? This is an extremely common box size.. How can this still be an issue? The only large flat rate box showing is for "game board" and is the wrong size.. People saying that they saw it must be selecting game board size because it is not there.

3 0 1

This issue still is occurring as of December 20th, 2021. 

Shopify Partner
775 30 90



There has been a few queries related to this issue. Some of the merchants are able to get the Large Flat Rate Box option and some of them are not. Have you tried contacting Shopify support regarding this issue?


One of the work around for this issue is to add a custom box with the same dimensions as of the Large Flat Rate Box and then set it as the default box so that, this box will be used to calculate the shipping cost. But yes, there will be issues with accuracy in the shipping cost since it is a UPS-calculated box price.


One of the other option is to use an app if you are open to using one. You can have a look at the Multi Carrier Shipping Label app that helps you add USPS carrier and choose the Large Flat Rate Box to handle the shipping process. The rates will be displayed at checkout based on this and the shipping label can easily be generated with accurate shipping cost. You can even automate the tracking process for the USPS orders by sending out live tracking emails to your customers.  

Customer Success @ PluginHive
Shipping Automation | FedEx shipping | Multi-carrier shipping | Shipment Tracking | Australia Post shipping