Skip to content
Visit ShipperHQ.com
  • There are no suggestions because the search field is empty.

USPS Flat Rate Box/Envelope Methods

Set up USPS Flat Rate shipping with accurate box configurations and rate display options

Overview

USPS Flat Rate methods are ideal for merchants who want consistent, fixed shipping rates using predefined USPS box and envelope sizes. These methods rely on box dimensions and require Dimensional Packing to be enabled in ShipperHQ.

Before using USPS Flat Rate methods, confirm that your boxes are correctly configured and that dimensional packing is active.

Setup

    1. Enable Dimensional Packing

      • Go to Advanced Features → Dimensional Packing and make sure it’s enabled.

    2. Add USPS Flat Rate Boxes or Envelopes

      • Go to Boxes and click Add New Box.

      • In the Basic tab, use the Box Size dropdown to select a predefined USPS Flat Rate option (e.g., Small Flat Rate Box, Medium Flat Rate Box, Flat Rate Envelope).

    3. Activate USPS Flat Rate Methods

      • Go to USPS Carrier → Basic → Active Shipping Methods.

      • Add the corresponding methods for each Flat Rate box you plan to use.

        • Example: Add USPS Small Flat Rate Box if you’re using the Small Flat Rate Box.

    Once configured, USPS will automatically display the correct Flat Rate method when the corresponding box is used.

    Note: USPS enforces specific box dimensions. If your box dimensions don’t match their standards, Flat Rate methods won’t appear.

    Carrier Configuration

    Example: If a product measures 8 × 4 × 1 and you have USPS Small, Medium, and Large Flat Rate Boxes configured, USPS will show all three options at checkout, since the product can fit in each.

    To show only the cheapest Flat Rate method:

    1. Go to USPS Carrier → Basic → Account Settings.

    2. Enable Show Cheapest Flat Rate.

    With this enabled, only the least expensive Flat Rate option (e.g., USPS Priority Mail Small Flat Rate Box) will display at checkout, while Medium and Large options are hidden.

    If you want to hide all other USPS methods when a Flat Rate box is chosen, create a Box-Based Shipping Rule to control which methods appear.