U.S. Postal Service STD-4C Specification Information


Effective October 5, 2006, all new designs approved for NEW CONSTRUCTION AND MAJOR RENOVATION require U.S. Postal Service STD-4C compliant mailbox systems.  The new USPS-4C Standard includes the following specifications:

  • A new minimum size requirement for mailboxes (12″W x 15″D x 3″H).

  • A parcel locker requirement based on a 1:5 parcel locker to customer compartment ratio (effective July 2020).

  • Strengthens security requirements for the units.

  • Standardizes and improves tenant compartment lock design.

  • Adds testing requirements to verify acceptability for either indoor or outdoor use.

  • Meets Americans with Disabilities Act (ADA) standards.

USPS Height Regulations


Installation/Layout Instructions specified in USPS Standard 4C – pages 53821-53832 of the above referenced USPS 4C Standard “Notes” sections specify:

All 4C Units shall be designed such that they are in compliance with the following installation requirements:

  1. The floor of the lowest patron mailbox shall be no less than 28″ above the finished floor (AFF).
  2. The patron lock in the highest mailbox shall be no more than 67″ above the finished floor.
  3. The USPS Arrow lock (master door lock) opening must be a minimum of 36″ and a maximum of 48″ above the finished floor.
  4. The floor of the lowest parcel locker shall be no less than 15″ above the finished floor.

  5. The master access door(s) must be allowed to open a minimum of 90 degrees with no obstruction.
  6. There must be at least one parcel locker for every (5) five patron mailboxes in installations of (5) five or more patron mailboxes.There is no requirement for parcel lockers in installations of less than (5) five patron mailboxes, but one or more parcel lockers are recommended.