Confused by all the different shipping options??? You're not alone. I go to the post office and see scores of confused customers looking at overpriced supplies and paying too much to ship items too slowly. Here I compare 6 different USPS flat-rate shipping containers.

The variety of Flat-Rate shipping options that the USPS offers has grown considerably in the past few years. So quickly that paypal has not kept up with the change in shipping classes.  Custom size boxes can be expensive, so a good reason to use USPS shipping is to allow you to customize the packing material, and use a standard (Free!) box from USPS.   I have included the part number below to help you ordering free shipping supplies from the post office website.
 
Here are a few of the Flat rate shipping options I use most often with USPS part number and APPROXIMATE online shipping cost without insurance (as of 19 Jan 2009)


Flat-Rate shipping options ( Prices Jan 09)
Priority            Domestic            International    USPS Part                     Notes
Envelope            $4.80                    $12.30      EP 14-F                         Economical choice- Caveat emptor-no insurance available, no indemnity.*
Small box           $4.80                    $12.30      O-SMALL-FRBX         Great for small electronics, cell phones, PDAs other small, flat items
Regular box1     $9.85                     $39.85      O-FRB1X                       Excellent for large number of small items, or small books
Regular box2     $9.85                     $39.85      O-FRB2X                      Flatter box than FRB1- Great for over-sized books. Pack large items well!!
Large box         $13.50                    $51.25      LARGE-FRBX              Don't use this one much.. it may be easier to split into smaller shipments?

Express
Envelope           $16.63                   $25.71       EP 13-F                         Good choice for small items that need to be insured.**

Notes:
* The flat-rate Priority Envelope is great for international postage paid online becuase the customs form is the Label. This saves 3 extra sheets of paper because you don't have to fill out the whole declaration in triplicate.
**The cost with insurance can sometimes be cheaper with an Express mail flat-rate than with Priority Mail. Be sure to check the Total shipping costs when comparing options.

Click on the flat rate section of the USPS Postal store site and you can easily add these to your cart for free!!


Customize your Packing Materials- Not the box.
When you take in to account the cost of buying boxes on your own, it is clear that it is often easier to design your packing around the USPS shipping boxes that can be ordered online for free. Even a nominal cost savings can add up over time, especially when you consider the time involved with packing, measuring, and entering container dimensions into PayPal or USPS shipping programs.

Flat-Rate is Faster
Bonus: for many shipping classes flat rate is faster because you know the dimensions of the box from the USPS website, and you don't have to weigh the box for domestic shipments. So there are four less items to type into the computer when you are busy with shipping!