Priority Mail: by Weight or Flat Rate?

Go To Great Panes, Kathryn Maloney ©2009

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Domestic Priority Mail:

When are flat rate boxes better than shipping by weight?

While we use First Class Mail whenever possible, sometimes you need to ship Priority. Boxes are free from USPS and they’ll even ship them right to your door for free if you order them online: Priority Mail Boxes

Domestic Priority Mail rates change based on shipping zones, unless you are using their Flat Rate Boxes (good for up to 70 pounds). Sometimes the flat rate boxes are a good deal–sometimes it’s better to ship Priority Mail by weight.

Small Flat Rate Box & Flat Rate Envelope (same price):
These cost the same as the “up to 1 pound rate” for Priority packages regardless of the zone they are being shipped to. If your items are going Priority and fit in this package, you’ll get the best Priority rate possible.
Envelope: 12-1/2″ x 9-1/2″
Small Box: 8-5/8″ x 5-3/8″ x 1-5/8″

Medium sized flat rate boxes (formerly the “regular” size):
Comes in two shapes:
Medium Box 1: 11″ x 8-1/2″ x 5-1/2″
Medium Box 2: 13-5/8″ x 11-7/8″ x 3-3/8″

Shipping by weight cost is better than using the medium box for these packages:
$8.70: Up to 2 lb, shipping to all zones.
$9.90: Up to 3 lb, shipping to zone 6 or closer.
$9.45: Up to 5 lb, shipping to zone 4 or closer.
$10.30: Up to 7 lb, shipping to zone 3 or closer.
$9.90: Up to 10 lb, shipping to zone 2 or closer.

Large sized flat rate box:
There are two different boxes, both the same size–one is especially for shipping to APO/FPO Destinations ($11.95), it has a lower price than the one for all other addresses.
Large Box: 12-1/4″ x 12-1/4″ x 6″

For non-APO/FPO destinations:

Shipping by weight is better than or equal to using the large box for these packages:
$11.95: Up to 3 lb, shipping to all zones.
$12.95: Up to 4 lbs, shipping to zone 7 or closer.
$13.75: Up to 5 lbs, shipping to zone 6 or closer.
$13.95: Up to 9 lbs, shipping to zone 4 or closer.
$13.30: Up to 11 lbs, shipping to zone 3 or closer.
$13.95: Up to 19 lbs, shipping to zone 2 or closer.

The flat rate box is always less expensive for these packages:
$14.30: 19 lbs and up

You can see USPS Priority Mail shipping chart and the rates and compare for yourself here:

Priority Mail Postage & Labels Online

You get a discount for paying for your postage online, and for Priority packages you get free delivery confirmation! You can buy postage for all the flat rate boxes through’s Click ‘n Ship.

Paypal only offers postage for the flat rate envelope (not the small box, though they are the same price and I use that label for the small box, which might be risky since the label says it’s for an envelope…) and the medium (formerly the regular) sized flat rate box. More on Paypal shipping here: Shipping Through Paypal

For more shipping tips see our main “Shipping” page–see the gold links on the right or click here:
Shipping Basics

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One thought on “Priority Mail: by Weight or Flat Rate?”

  1. We have been using flat rate shipping since it first came out and it seemed to be cost effective. With all the increases it doesn’t seem so anymore. Does anyone remember what the first flat rate box was. I have tried to google it but the information doesn’t seem to exist.

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