USPS Flat-rate Price Comparisons

We were curious to know how good a deal the USPS flat-rate boxes were, so I went over to their online calculator and ran some comparisons. The Priority Mail boxes come in three price categories across five box shapes (don't forget that the USPS changes this stuff all the time):

Large:
    23-11/16" x 11-3/4" x 3"    (835 cu in)    $22.65 (2.7 cents/cu in)
    12" x 12" x 5-1/2"              (792 cu in)    $22.65 (2.8 cents/cu in)

Medium:
    13-5/8" x 11-7/8" x 3-3/8" (546 cu in)    $16.25 (3.0 cents/cu in)
    11" x 8-1/2" x 5-1/2"         (514 cu in)    $16.25 (3.2 cents/ cu in)

Small:
    8-5/8" x 5-3/8" x 1-5/8"     (78 cu in)      $9.20    (11.8 cents/cu in)

First, the small box is by far the worst deal by volume, although who cares if you have something smaller to ship.

Now, let's consider what it would cost to ship similar sized boxes at the same priority postage rate for something about the size of the large and small boxes above to book end the comparison. I'll work with the following two custom box sizes:

My Large Custom Box -- 23" x 12" x 3" (828 cu in)

My Small Custom Box -- 9" x 5" x 1.75" (79 cu in)

When shipping a custom box, USPS charges based on distance, weight and size. It's a complicated formula that is completely different than the fixed-rate boxes, making it hard to do a simple comparison, but I'll do my best to give you a sense of it.

Since weight it such a big part of the equation, let's look at an empty box--let's call that 5 oz. Then, we'll look at a box filled with books. Paperbacks weigh about 0.5 oz/cu in.

The cheapest thing you could do custom is to send a small custom box within your same zone. With smaller boxes--those with no side longer the 12 inches, the prices for a 5 oz box is $7.95. For our small box filled with 40 oz of books, you'd pay $9.30, just a dime more than the standard post office small box.

Everything changes with distance. A coast-to-coast box (say MA to CA) is much more expensive:

My Large Custom Box:
    Empty at 5 oz                          $10.65 (1.3 cents/cu in)
    Filled with 3 lbs of stuff         $21.15 (2.6 cents/cu in)
    Filled with books at 414 oz    $97.20 (11.7 cents/cu in)

Small Custom Box
   Empty at 5 oz                          $10.65 (13.5 cents/cu in)
   Filled with books at 40 oz      $21.15 (26.8 cents/cu in)

A lightly filled large custom box is less expensive than the standard USPS box, but gets more expensive fast. The breakeven point for the large box is 3 lbs, which would cost you $21.15. Interesting that the USPS small box is always less expensive going coast to coast.

If you want to save money shipping a package there are other shipping options than Priority Mail. The post office doesn't make those other services easy to find, in fact there's no way to do the less expensive options on-line--you'll have to go into a post office and ask for them. Looking at our large box of books, we'd get:

First Class Package Service (1-3 days): Not available over 13 oz.
USPS Retail Ground (2-8 days): $81.10
Media Mail (2-8 days): $18.94

And, if you really want to get it there fast, there's always Priority Mail express, which has a 1-2 day promise for $195.45.