A USPS order set to First Class Mail will not process when the package is over the First Class size or weight limits. The order errors at process time because the package does not qualify for First Class.

USPS First Class limits

  • Letter: up to 3.5 oz.
  • Large Envelope / Flat: up to 13 oz, no larger than 12 in x 15 in x 3/4 in.
  • First Class Package: up to 15.999 oz, and 108 in combined length plus girth.

A package heavier or larger than these (for example 2 lb / 32 oz) does not fit any First Class category, so the service cannot be used.

Fix

  1. Check the package weight and size against the limits above.
  2. If it is over 15.999 oz or larger than a flat, change the service to USPS Ground Advantage (it includes tracking and delivers in 2 to 5 business days).
  3. To keep First Class, reduce the piece to a flat within 12 in x 15 in x 3/4 in at 13 oz or less, or to a package under 1 lb.
  4. Reprocess the shipment on the corrected service.

What you should see

The order rates and prints a label once it is on Ground Advantage (or reduced within a First Class category), and the shipment shows the corrected service.