United States Postal Service Mailbox Regulations and Specifications

United States Postal Service Mailbox Regulations and Specifications

USPS Mailbox Height Guidelines for Installing Commercial Mailboxes

USPS Mailbox Height Guidelines for Replacement and Retrofit Mailbox Installations

USPS Mailbox Height Guidelines for Installing Residential Mailboxes

USPS National Delivery Planning Standards (PDF) includes 1 parcel locker to every 5 mailbox compartments requirement (1:5 ratio) - see page 13 (effective July 2020)
USPS Standard 4B/4B+ (PDF) applies to 4B/4B+ Horizontal and Vertical Mailboxes (standard for replacement and/or retrofit installations (effective October 2006)
USPS Standard 4C (PDF) for new construction and replacement information of existing equipment
USPS Standard 7C (PDF) applies to Curbside Mailboxes (effective September 2015)

Guidelines for planning and implementing mail service in new housing developments

How the US Postal Service STD-4C Regulation affects Centralized Mailbox Selection standard required for new construction (effective October 2006)
US Postal Service STD-4C Specification Information applies to 4C Horizontal Mailboxes (specifications 4C mailboxes must meet)

Guidelines for Upgrading or Replacing Your Commercial Mailboxes

ADA Compliance Guidelines-for 4C Horizontal Mailboxes
ADA Compliance Guidelines-for Cluster Box Units

USPS Standard 4C (PDF) for new construction and replacement information of existing equipment

USPS Mailbox Height Regulations for Installing Commercial Mailboxes

Commercial mailboxes for USPS delivery include Cluster Box Units (CBU’s), 4C Horizontal Mailboxes, 4B+ Horizontal Mailboxes and 4B+ Vertical Mailboxes. These products are commonly used in apartment complexes, commercial buildings, residential developments, condominiums and several other applications. 

Salsbury Industries manufactures USPS STD-4C Horizontal mailboxes that are required for new construction and major renovations. Salsbury 4C Horizontal Mailboxes must be installed according to postal regulations including the mailbox height requirements listed below:

USPS Mailbox Height Regulations for Installing Commercial Mailboxes
  • 67”- The tenant lock in the highest mailbox shall be no more than 67” above the finished floor.
  • 48”- The USPS Arrow lock (master door lock) opening shall be no more than 48” above the finish floor. In compliance with ADA regulations, the high forward and high side reach shall be a maximum of 48” above the finished floor.
  • 36”- The USPS Arrow lock (master door lock) opening shall be a minimum of 36” above the finished floor.
  • 28”- The floor of the lowest tenant mailbox shall be no less than 28” above the finished floor.
  • 15”- The floor of the lowest parcel locker shall be no less than 15” above the finished floor.  In compliance with ADA regulations, the low forward and low side reach shall be a minimum of 15” above the finished floor.

Easy Installation Mailboxes Compliant with USPS Height Regulations

The Salsbury Cluster Box Unit’s (CBU’s)  provide a convenient means for installation that complies with USPS regulatory mailbox height requirements. Salsbury CBU’s include a pedestal and all CBU’s meet USPS mailbox height requirements. Check with your local postal authorities for official approval on mailboxes for your project.

How Do USPS Mailbox Regulations Affect Buying Centralized Mailboxes?

Different wall mounted mailboxes are in USPS compliance with different projects.  If your mailboxes are being used for new construction or major renovations, the 4C Wall-mounted Mailboxes or free-standing Cluster Box Units (CBU’s) can be used. For replacement and retrofit installations, the 4B+ Horizontal Mailboxes or 4B+ Vertical Mailboxes can be used. If the rough opening will change, then the 4C Horizontal Mailboxes must be used. Make sure to contact your local postmaster for details on the appropriate mailbox for your project. 

USPS Mailbox Height Guidelines for Replacement & Retrofit Mailbox Installations

A “major renovation” would occur anytime the condition of the wall is being modified where the existing wall-mounted mailboxes are presently installed. Commonly used mailboxes for replacement and retrofit installations are the 4B+ Horizontal Mailboxes and the 4B+ Vertical Mailboxes. If the rough opening of the wall is modified, the renovation would be considered “major” and mailboxes complying with the new USPS STD-4C regulation should be installed. If you have any questions about which USPS mailbox standard should be applied to a specific project requiring “USPS Approved” mailboxes, please contact your local Post Office for assistance prior to purchasing your mailboxes.

Postal Regulatory Heights for the 4B+ Horizontal Mailbox and 4B+ Vertical Mailbox

Both the 4B+ Horizontal Mailbox and the 4B+ Vertical Mailbox must be installed in compliance with USPS Regulations. When installing the unit, you must have no less than 28” from the finished floor level to the bottom of the lowest row of mailboxes and no more than 67” from the finished floor level to the tenant locks on the top row of the mailboxes. The postal access door is allowed to open a minimum of 90 degrees with no obstruction. The master lock opening must be a minimum of 30” and a maximum of 58” above the finished floor.

Front View of 4B+ Horizontal and Vertical Mailboxes in Wall
  • 67”- The tenant lock in the highest mailbox shall be no more than 67” above the finished floor.
  • 58”- The USPS Arrow lock (master door lock) opening shall be no more than 58” above the finish floor.  In compliance with ADA regulations, the high forward and high side reach       shall be a maximum of 58” above the finished floor.
  • 30”- The USPS Arrow lock (master door lock) opening shall be a minimum of 30” above the finished floor.
  • 28”- The floor of the lowest tenant mailbox shall be no less than 28” above the finished floor.

USPS Mailbox Height Guidelines for Installing Residential Mailboxes

USPS Approved Residential Mailboxes

Curbside and roadside mailboxes must be easily accessible to the mail carrier. By USPS regulatory standards, your mailbox should be 41” to 45” from the ground or street surface and up to the inside floor of the mailbox. Your mailbox door should be set 6” to 8” back from the front face of the curb or the edge of the road. If you do not have a raised curb remember to contact your local postmaster for proper guidance.

USPS Mailbox Height Guidelines for Installing Residential Mailboxes

USPS mailbox regulations apply for Post Mounted Mailboxes and Locking Mailboxes.

  • Mailbox height must be 41”- 45” from the surface of the road or point of entry.
  • Mailbox must be 6” to 8” back from the curb.

USPS Mailbox Regulations for Locking Mailboxes

USPS Approved Locking Mailboxes

Locking Mailboxes have become a popular choice for individuals looking for added security for their mail delivery. All curbside locking mailboxes must meet the same functional requirements as standard mailboxes and must be approved by the postmaster. Salsbury Industries offers several Locking Mailboxes that are USPS approved. See below for notes on USPS locking mailboxes:

  • Do not rely on USPS carriers to open locked mailboxes as they do not accept mailbox keys.
  • The slots for the incoming mail must be at minimum of 1.75 inches high by 10 inches wide.
  • Slots on locking mailboxes must be able to hold the residents daily volume of mail.
  • The slots must be large enough to accommodate any unfolded USPS Priority Envelopes.

USPS and Private Delivery Mailboxes

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