What's USPS First Class Package max weight and dimensions?

[poroscarodr]

I found info on the internet saying max 15.99 ounces and 22 in long, 18 wide, and 15 thick. I tried changing weight and dimensions in my seller dashboard and when I exceed 15.99 ounces it tells me something like "choose priority mail instead", but when I change dimensions it won't notify me it no longer qualifies for first class.

I even put 100x100x100, and it still let me save changes, so, what's really the limit? thank you

[buyselljack2016 · Accepted solution]

@poroscarodr 

The dimensions that that you found are correct.

You can put in the 100", but you would not be able to purchase a 1st Class label.  It would fail.

Been there, done that.  Just today, or was it yesterday. I was changing a dimension from 6 to 4, but ended up putting 64.