It is time to choose the correct length mailbox post for your project. What are the factors that need to be considered when making the choice?

USPS Guidelines

According to the USPS the following guidelines need to be adhered to when installing a mailbox: 

  • The incoming mail slot should be between 41" to 45" above the road surface
  • The mailbox needs to be set back between 6" to 8" from the curb. For non raised curb application this may vary based on your locality and the local postmaster will provide additional information. (fig a.)
  • The post depth should not exceed 24" (fig b.)
  • The post material should provide a stable mounting platform but bend or fall away in case it is hit by a car to avoid injury

USPS Mailbox Guidelines

How do I Choose the Correct Mailbox Post Length?

Depending on the manufacturer and mailbox type there will only be one length available. This is generally the case for non locking mailboxes which come with In-Ground mounted posts.

For locking mailbox which also have the option to be surface mounted there may be multiple lengths available. A great example are Mail Boss mailboxes which offer surface mounted posts in lengths of 27" and 38". 

To further complicate the issue the incoming mail slot is not at the bottom of the mailbox but generally half way up from the bottom of where the mailbox is mounted and this additional distance must be factored in when selecting the correct length. For the Mail Boss Mail Manager this distance is around 4.9" as highlighted in the red area in the specifications below.

Mail Boss Mail Manager Specifications

The Calculation for Surface-Mounted Posts

(Curb height) + (Post Length) + (Incoming Mail are height from bottom of mailbox) = Total Length 

If we use the example above with the 27" post then the bottom of the incoming mail area will be just below the 41".

6" + 27" 4.9" = 37.9" 

In this case it would be recommended to reach out to the local postmaster to ensure they are ok with the slight deviation though the incoming mail area (just not the bottom area) does fall within the guidelines.


*** This advice does not supersede USPS guidelines in any way. You must always contact your local postmaster and approval prior to installing a mailbox ***

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