This is a replacement USPS shipping estimation extension. As of 25 Jan 2026 the included USPS extension for opencart will no longer function. This is a drop in replacement BUT you need to get your Consumer Key and Consumer secret in order to use this extension.
This extension does mostly weight based estimate with a little logic to account for larger sized packages.

This extension is provided for free to maintain the spirit of the original OpenCart 2.3.x.x release. Since the default USPS module is now obsolete due to USPS system changes, this "drop-in" replacement allows you to keep your store running on OC 2.3.x.x.

NEW OC 3.x.x.x version.
Note: The 3.x.x.x version is new and tested but if there are issues, let me know!