Mailbox Dimensions (Standard & USPS Sizes)

Here’s our mailbox dimensions resource guide, including the standard large, medium, and small USPS box sizes, brick designs, and installation measurements.

Mailboxes can come in a wide range of shapes and sizes. This is why it can be challenging to know exactly what’s right for you. Whether you need a larger postal box for your orders and packages for your business, you need to replace your old postal box, or you want to install your first one, it’s important to get the right size to fit your needs.

Standard Mailbox Dimensions

Every mailbox in the United States must be approved by the standards of the United States Postal Service (USPS). T1 or C1 size (small mailbox) is about 5″ wide and 6″ tall and 18 ½” long.

Then, there is T2 or C2, which is about 6″ wide by 7″tall and 19″ long (medium). Finally is the T3 or C3 size (large) which is about 8″ wide by 11 ½” tall and 22 ½” long. (T means traditional, and C stands for contemporary.)

Large Mailbox Size

Residential property owners can still use large mailboxes, and even commercial properties can benefit from its extra space. Magazines and newspapers don’t need to be rolled to fit inside large boxes because they have extra room for them inside.

The standard large mailbox is designed to hold a parcel that measures 8 by 11 ½ by 22 ½”. One side of it is lying flat on the box floor. The measurement of the inside width at the bottom is 10 1/2″ and 130 square” for the minimum door or slot opening.

Typically, large postal boxes measure 12 to 20″ tall, 10 to 20″ wide, and 6 to 20″ deep. They can be installed at a driveway’s end with a post.

Medium Mailbox Size

Medium sized mailboxes are slightly larger than small sized units. People who are subscribed to different magazines and newspapers and love online shopping opt for medium sizes, which are installed either on a post or mounted on a wall.

Typical medium mailbox dimensions are 6 to 20″ tall, 6 to 20″ wide, and 10 to 20″ deep.

Average medium box sizes can accommodate small boxes, envelopes, rolled magazines, rolled newspapers, bundled mails, padded documents, and padded envelopes. They can hold things that a small box can accommodate, even small packages.

Small Mailbox Sizing

Homeowners who don’t receive much mail or packages opt for small mailboxes.  They don’t have a lot of newspaper or magazine subscriptions and rarely receive mail as well.

A small postal box is just perfect for them because it can accommodate two rolled magazines and newspapers and up to 15 standard letters.

Like other types of mailboxes, it can be installed on a post or the wall. The average sizes of small mailboxes are approximately 12″ tall, 5 to 19″ wide, and 4 to 14″ deep.

Brick Mailbox Measurements

A brick mailbox’s primary design involves a concrete block core and a decorative brick veneer and has a side opening that faces the street. This opening is large enough to accommodate a standard mailbox.

A brick postal box can provide a durable and strong structure to your property. One can also add curb appeal and requires less maintenance.

For their dimensions, masonry mailboxes shall not be more than 24 by 24 inches or two feet and no more than 5 feet tall.

Its front edge shouldn’t be set closer than 15″ from the curb’s rear edge or within 2 feet of the Buffalo box. Its front shouldn’t be closer than 6″ nor farther than 15″ from the curb’s rear edge.

Mailbox Flag Dimensions

A flag, which is also called the carrier signal flag, on the side of the box alerts couriers that there is outgoing mail in the box. A universal outgoing mailbox flag typically measures about 8.25″ tall and 1.25″ wide.

For the color, a carrier signal flag can be any color, preferably fluorescent orange, except shades of white, blue, yellow, and green. This color should also have a contrast with your mailbox’s predominant color.

However, carrier signal flags shouldn’t be mounted anywhere you want. The USPS requires they’re on the right side when looking at it from the front.

Mailbox Mounting Board Dimensions

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Depending on the manufacturer, a steel postal box mounting board, for instance, can have sizes of 0.8-inch high by 6.1″ wide by 11.8″ deep. It can be installed on a four by four hollow post or wood.

Meanwhile, another example is a plastic postal box mounting board that measures 1.1″ high by 6″ wide x 12.5″ deep. It can fit different sizes of post mount mailboxes and mounts to a four by four inches plastic or wooden post.

How Tall Is A Mailbox Post?

Let’s take a four by four mailbox for example. The bottom of the box must be between 41 and 45″ above the highway shoulder or road surface, according to USPS standards.

The total height is approximately 45″, the bottom is 42″ from the ground, and a few inches added by the curb. 

How High Does A Mailbox Have To Be?

The standard height of a mailbox should be between 41 and 45 inches, per the standards of the USPS. 

How Far Should A Mailbox Be From The Road?

Mailboxes should be installed between 6-8 inches away from the curb, according to the USPS, because it can keep couriers from pulling off the roadside if it is closer than six inches to the curb.

On the other hand, installing one more than 8″ away from the curb makes it hard for a courier to reach it.

Apartment Postal Box Dimensions

The USPS also set rules and standards on how high landlords can install a mailbox. The mailboxes’ bottom row should not be lower than 28″ from the floor, with the parcel lockers the only exception. They can be installed at least 15″ from the ground.

On the other hand, the top row of apartment mailboxes shouldn’t be more than 67″ high to allow the average height tenants to reach them.

For the mail compartment size, a standard apartment postal box shouldn’t be smaller than 3″ (H) by 12″ (W) by 15″ (L). The USPS regulations accept anything larger than these sizes.

USPS Box Dimensions

Curbside residential mailboxes should be six to 8″ away from the curb and have a slot or door that is 41 to 45″ from the ground.  Posts must not be larger than 4 by 4″ and can be made of aluminum or steel at most 2″ in diameter.

The standard small mailbox dimensions should be 5 x 6″ (WH) and 18″ (L). Meanwhile, a medium box should be about 6 x 7″ (WH) and 19″ (L). On the other hand, a large box should be about 8 x 11 ½” (WH) and 22 ½” (L).

T4 Mailbox Measurements

If you receive large packages or run a business sending a lot of them, an extra large or T4 mailbox can be for you. It can hold a lot of daily mail if you choose it for your mail deliveries.

Homeowners who want to store their incoming inventory may also opt for a T4 postal box, which can be positioned to the side of the porch or installed at the end of the driveway on a post. 

Their average measurements are from 20 to 40″ (height), 15 to 40″ (width), and 10-17″ (depth).

These are the important sizes to remember for homeowners looking to install or use an extra large mailbox to suit their equally large needs.

For more related content, visit our gallery of the types of fences on this page.