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How to get started

Warning : The settings on this page are based on a new version of USPS that has not be openly release yet.

To start using USPS, lets start by going to the Shipping tab under Store in the Wordpress Settings area. Next, click the "edit" link to the right of "USPS", the settings will appear to the right of the service selection.


This ID can be obtained by going here. Fill out the form and you will receive a response from USPS with your API User ID. By default, you will only have access to the "development" server, you need to follow the instructions in the email that they sent you and email them back to get "Production" access. You will not be able to use the shipping module unless you have production access !

Insuring your shipment

Insure value of the cart: Check this box to add the insurance fee for your shipments through USPS.

Due to how this is implemented, it is not guaranteed to be accurate. I am working on a proper solution for this.

Advanced Rates

Warning, there be dragons!!

Advanced rating is very misunderstood, I hope to clear up some issues. When you select advanced rating, the shipping module will rate as if you were going to ship out each individual item in the cart as if it were alone.

If someone were to order 5 apples and 1 orange, the shipping module would rate 6 packages.

You may be asking, why is this necessary ? Well, sometimes a store has a lot of items that have odd shapes and USPS will add additional fees for handling those packages, advanced rates will send dimensions in addition to the weight.

Under Advanced Rates, you can individually select advanced rates for Domestic and International shipments.

Select Services

All of the possible services that you can use through USPS are listed in this box. It is strongly recommended that you use the smallest number of options to not confuse your uses and choose the most accurate to your usage. Click Here to view the list of services with some additional information.

Note: The services displayed to the user vary depending on weight and or dimensions of items in the shipment, your selections here will determine whether or not the service is displayed if available for the shipment.

For the most average user, I would suggest the following services:

Express Mail First-Class Mail Priority Mail

For international, Express-mail International Priority Mail International First-Class Mail International First-Class Mail International Package

Container Type

This should be left as Variable unless you fully understand what you are doing! Below I have explained these values.

Variable : Most shops will ship in varying sized/shapes packaging, this means just that. This is the default and should rarely be changed. Rectangular : This means that all of your packaging is Rectangular, if this is always the case, this may be safe but must always be true to keep accuracy! Nonrectangular : As above but for non-rectangular packaging Flat Rate Box : If your store Only ever uses flat rate boxes, use this, if you ever package in your own or other packagin, DO NOT Use. Flat Rate Envelope : As above but using the envelope mailer instead of a box

Select Free Services

Any services you select in this area will show up as free when the service is eligible. You can select as many services as you like.

There currently isn't a way to control when the free services kicks in.

Additional Fees

A common request has been to offer adding an additional fee to the shipping rates. This addition does not add a line-item on checkout but adds to the individual shipping rates. You can set a fee for domestic and international rating separately.


I have added a new feature that allows you to test if your USPS credentials are correctly configured. There is a new check box next to "Perform Test", select this and save the settings. The USPS settings page will have a response regarding what happened with the API request. If everything worked you should see "Your API credentials are working properly", if you don't get this message, there is something wrong. There are several error messages possible:

1. A USPS User ID is required for this module to work, you have not entered one

If you receive this message, please enter a valid USPS API user ID into the field.

2. A base postal code is required for this module to work, you have not entered one

If you receive this message, please enter your postal code near the top of the "Shipping" settings page.

3. There is a problem connecting to the USPS web service Error::

This is most likely an issue with the server that you are hosting your website on. This error will be very technical. If you are getting an error here you do not understand, please contact me via my contact form Here and include your error in the message. 

4. USPS responded with the following error

The error here should provide some insight into what is happening. They can often be very technical and if you do not understand them, do not fret! Just contact me as explained above.

Example of the settings

Usps v3 annotated.png