Lara......it really isn't going to change the rate if you put 1" or 3"....espeically for 1st class items, once someone buys enough to make it over 16 oz. it goes to a Prioirty rate.
Are you talking about items less than 1 lb for first class?
If so, dimensions probably don't matter that much unless quite a few are purchased.
In my pet prodcut shop, I sell dog coats and goat coats and I usually just use a 6x4x2 or a 7x5x2 size for all of them.....
I know even if 4 or 5 are bought, the package is not going to need to be oversize.
I tend to put slightly smaller measurements if a non-breakable item than if a fragile item. To big of dimensions and the calculator might see several items needing to be in an oversize box.
On my goat coats at first I was using the box size a 12x8x3 but if someone bought 2, it would calculate as an oversize box which it should not since I can put 2 in a 12x9x4 box.
So I figured out what size I needed to put so it wouldn't figure oversize and these work out just fine (even though they really measure closer to that box size).
It's a little hard to get the size part figured out so it doesn't figure oversize but once you figure out what it takes, it's fairly easy.
I've found it helpful as have other members that have been using this awhile to have Internet Explorer open and also Chrome....that way if you're signed in on IE you can go to Chrome and "shop" and add different items to your cart to see the shipping cost.
I also changed the zip code for zips in CA and my zip here in NC to get a range of costs to compare with on USPS to see if it's doing ok.
