Most residential mailbox posts are a 4 x 4 inch wood post or a 2 inch steel or aluminum pipe, the two supports USPS recommends. The right length is simple math: the part above ground must put the mail entry 41 to 45 inches above the road, and the part below ground should be no more than 24 inches. Surface-mount posts skip the buried part and are shorter.
This guide walks through post materials, in-ground versus surface mount, and how to calculate length for your site, so you buy the right mailbox post the first time. If you also need the box, a mailbox and post package comes already matched.
Mailbox post dimensions at a glance
| Measurement | Typical value | Source |
|---|---|---|
| Post cross-section | 4 x 4 in. wood (3.5 x 3.5 in. actual) or 2 in. diameter steel/aluminum pipe | USPS |
| Mail entry height | 41 to 45 in. above the road surface | USPS |
| Door setback | 6 to 8 in. behind the curb face or road edge | USPS |
| Maximum burial depth | 24 in. | USPS / Federal Highway Administration |
| Steel in-ground post | 43 in. long, 12 in. buried, top about 31 in. above the street | Mail Boss |
| Steel surface-mount post | 27 in. (the usual pairing for the base plate) or a taller 37/38 in. version | Mail Boss |
The USPS figures are on its How to Install a Mailbox page. Your local postmaster can adjust them, especially where there is no raised curb, so check before you cut anything. Our guide to how high a mailbox should be covers the edge cases.
Types of mailbox posts
| Post type | What it is | Good for | Trade-offs |
|---|---|---|---|
| Wood 4 x 4 | Pressure-treated lumber, cut to length | Budget installs, standard curbside boxes, breakaway-friendly | Rots at ground level without gravel drainage; needs a mounting plate or platform |
| Steel | Galvanized, powder-coated square tube with a mounting top | Heavy locking mailboxes, high-theft areas | Usually set in concrete; heavier to handle |
| Aluminum | Cast or extruded aluminum, often a decorative sleeve over a 4 x 4 | Decorative curb appeal; does not rust | Most styles still need a buried wood core |
| Polyethylene, vinyl or PVC sleeve | A plastic shell with a support arm that slides over a 4 x 4 | Low maintenance, quick facelift over a new or existing post | Arm has box size and weight limits |
| Decorative and pedestal | Ornamental posts with brackets, finials or a single cast pedestal | Matching a specific mailbox line (Whitehall, Salsbury) | Often made for one mailbox family |
Wood 4 x 4 mailbox posts
A treated 4 x 4 is the default, and it is the core of many decorative posts too. It is light, easy to cut to exact length and gives way if hit, which is what USPS wants. Put gravel under it and keep the top of the footing sloped so water runs off.
Steel mailbox posts
Steel suits heavy, locking boxes. The Mail Boss steel post is galvanized steel with a powder-coated finish in black, granite, white or bronze, comes as a 43 inch in-ground post or 27 and 37/38 inch surface-mount posts, and bolts to Mail Boss mailboxes and spreader bars with 4 included bolts. Mail Boss buries its in-ground post 12 inches and sets it in concrete; the worked example below shows how that lands the mail slot in the USPS range.
Aluminum and decorative posts
Whitehall's Superior post is sand-cast aluminum and does not include the 4 x 4 or cement. In Whitehall's Balmoral instructions, the aluminum post slides over a buried treated 4 x 4 x 48 inch post and is fixed with two lag bolts. Whitehall's Balmoral instructions bury that wood core about 30 inches, deeper than the USPS 24 inch guidance, so ask your postmaster before copying that depth. Jayco's letter locker posts come in aluminum or stainless steel in a wide range of lengths: 60, 48 and 36 inch in-ground and 36, 30 and 16 inch surface mount.
Polyethylene and vinyl post sleeves
Sleeve posts give you a finished look without a custom build. Mayne posts are 100% polyethylene with UV inhibitors and install over a standard 4 x 4 wood post (not included). The Mayne Signature Plus takes a medium or large box at least 7 inches wide and under 16 lbs. See the full range in our Mayne collection.
In-ground vs. surface-mount mailbox posts
| In-ground | Surface mount | |
|---|---|---|
| Installs into | Soil, with concrete or tamped gravel and soil | Existing concrete: curb, sidewalk or driveway edge |
| Length | Longer: above-ground height plus burial depth | Shorter: above-ground height only |
| Hardware | Post plus concrete or gravel | Post plus base plate and masonry anchors |
| Best when | You have a lawn or gravel shoulder at the road | Concrete reaches the road edge, or you cannot dig |
The Mail Boss surface-mount post and base plate package is made to sit on a 4 to 8 inch sidewalk or curb, with a 10 gauge steel base plate. The plate is fixed to the concrete with 8 masonry anchors (typically 1/4 x 3 inch outdoor masonry screws, per the installation sheet), and the post bolts to the plate with 4 bolts. If you have soil but do not want to dig, a ground anchor is a third option: see how to install a mailbox post without concrete.
How to choose the right mailbox post length
Work out the above-ground height first, then add what goes underground.
Step 1: Find the target height
Aim for the middle of the USPS range, about 42 to 43 inches from the road surface to the bottom of the box or the mail entry. That leaves room for error either way.
Step 2: Subtract what sits between the road and the post, and between the post and the mail
The formula our original version of this guide used still holds:
Curb or grade height + post height above its base + distance from the post top to the mail entry = mail entry height (target 41 to 45 in.)
- Curb or grade height: how much higher the ground or sidewalk at the post is than the road. Zero if level; often 4 to 8 inches for a raised curb.
- Post top to mail entry: the thickness of the mounting plate, and on boxes with a front slot, the distance from the box floor up to the slot. Check the mailbox spec sheet. If your box sits directly on the post, you can usually measure to the bottom of the box instead.
Step 3: Add burial depth (in-ground only)
Add your burial depth, which should be no more than 24 inches. Many posts need less; Mail Boss buries its steel post 12 inches. For a wood post you will cut, add a few inches to trim.
Worked example: Mail Boss steel post (no cutting)
- The 43 inch post goes 12 inches below street level, leaving the top about 31 inches above the street.
- Mail Boss says the mail slot on its Mail Manager, Mail Boss and Package Master boxes is 11 to 13 inches above the box floor.
- 31 + 11 to 13 = a slot about 42 to 44 inches above the street. That is why a 43 inch post is the right length for these boxes.
- Need a deeper footing for frost? Mail Boss suggests bolting a treated 4 x 4 inside the base of the steel post and burying the wood, so the steel stays at height. Keep the total within 24 inches unless your postmaster agrees otherwise.
Worked example: wood 4 x 4 with the box on top
- Target: 42 inches to the bottom of the box, on level ground (no curb).
- Mounting platform on top of the post: 1.5 inches. Above-ground post height: 42 minus 1.5 = 40.5 inches.
- Burial depth: 20 inches. Total: 60.5 inches.
- Buy a 6 foot (72 inch) treated 4 x 4 and cut it after the post is set.
Arm-style posts work differently: the post rises above the box and the arm holds it out over the road, so the arm height, not the post top, sets the mail height. Follow the post maker's chart for the 4 x 4 length.
Surface-mount example
With a surface-mount post, there is no burial depth, and the curb adds height. Run the same formula: curb height + post height + box floor to slot. With a 27 inch Mail Boss post on a 4 inch curb and an 11 to 13 inch slot height, that is 4 + 27 + 11 to 13 = about 42 to 44 inches. On an 8 inch curb the same setup reaches 46 to 48 inches, above the USPS range, so measure your curb before you order and ask your postmaster if the math lands outside 41 to 45 inches. Mail Boss pairs its base plate with the 27 inch post as standard; check with us before choosing the taller post.
Posts for two or more mailboxes
Shared driveways and duplexes often put two to four boxes on one post with a spreader bar or a double arm. The same height and setback rules apply to every box. Mail Boss steel posts accept its spreader bars, and Mayne makes double versions of the Rockport and Newport Plus. Our guide to double, triple and quad mailbox posts covers layouts and post choice.
Mailbox post kits and accessories
A post kit usually means the post plus its bracket or arm and cap, but rarely the 4 x 4 core or concrete. Read each listing for what is included. Finishing pieces such as Whitehall post cuffs and finials, the Mayne Solar Cap and the Mayne No Dig Ground Anchor are in our mailbox post accessories. When you are ready to put it in the ground, follow our step-by-step mailbox installation guide.
Shop
Browse mailbox posts by material and mounting type, or contact us with your mailbox model and curb height and we will help you pick the right length.
Frequently asked questions
What size is a standard mailbox post?
USPS recommends a 4 x 4 inch wooden post or a 2 inch diameter steel or aluminum pipe. A nominal 4 x 4 measures about 3.5 x 3.5 inches, which is the size most sleeve-style posts are made to fit.
How long should a mailbox post be?
Long enough to put the mail entry 41 to 45 inches above the road, plus up to 24 inches buried. A wood 4 x 4 often works out around 5 feet, so a 6 foot post cut to fit is common. A Mail Boss steel post is 43 inches with 12 buried.
How tall should a mailbox post be above ground?
About 41 to 45 inches minus the height of the mounting plate and any distance from the box floor to the slot. If the ground at the post is higher than the road, subtract that too.
Is a metal or wood mailbox post better?
Steel is stronger and suits heavy locking boxes but usually needs concrete. Wood is cheaper, easy to cut and gives way more readily if hit. Many decorative aluminum and plastic posts are sleeves over a wood core.
When should I use a surface mount mailbox post?
When concrete runs to the road edge, such as a curb or sidewalk, and there is no soil to dig. The post bolts to a base plate fixed with masonry anchors.
******It is always recommended to contact your local postmaster prior to installation. While most of our mailboxes are USPS-approved your local postmaster may have specific preferences in terms of mailbox types and installation location******