Mailbox installation is a half-day DIY job for most homeowners. Call 811 a few business days before you dig, set the post so the mail entry ends up 41 to 45 inches above the road and the door sits 6 to 8 inches back from the curb, bury the post no more than 24 inches, then bolt the box on with the maker's hardware.
This guide covers both ways to do it: an in-ground post set in concrete or packed soil, and a surface-mount post bolted to a concrete curb or sidewalk. If you still need hardware, start with our mailbox with post packages, which ship the box, post and mounting hardware together, or pick a mailbox post for the box you already own.
Before you start: the USPS placement rules
The Postal Service publishes simple curbside guidance on its How to Install a Mailbox page and repeats it each year in its Mailbox Improvement Week bulletin. These numbers drive every measurement below.
| Rule | USPS guidance |
|---|---|
| Height | 41 to 45 inches from the road surface to the bottom of the mailbox or the point of mail entry |
| Setback | 6 to 8 inches from the front face of the curb or road edge to the mailbox door |
| Recommended supports | A 4 x 4 inch wooden post, or a 2 inch diameter standard steel or aluminum pipe |
| Burial depth | Bury the post no more than 24 inches deep |
| House number | On the box, in a contrasting color, in numerals at least 1 inch high |
The depth limit and the post sizes come from the Federal Highway Administration's breakaway advice, which USPS repeats in that bulletin: the ideal support bends or falls away if a car hits it, and heavy metal posts and concrete posts are examples of potentially dangerous supports. Some manufactured posts and pedestals come with their own depth instructions; we flag where they differ below. For the height details and edge cases, see our guide to how high a mailbox should be.
Two more checks before you buy anything: your local postmaster has the final say on placement (especially where there is no raised curb), and HOA or town rules may limit style, color or post material.
Tools and materials
- Tape measure and a marker or chalk
- Level (a post level that straps to the post is easiest)
- Post hole digger or narrow spade, and a digging bar for hard or rocky soil
- Drill/driver and socket set
- Gravel for drainage (about 6 inches in the bottom of the hole)
- Bagged concrete mix (Mail Boss calls for about 2 bags for its in-ground post), or none if you will tamp soil
- Scrap boards and clamps or screws to brace the post while it sets
- For surface mount: hammer drill, masonry bit and masonry anchors sized for your base plate
- The post, the mailbox and its mounting hardware, and reflective house numbers
How to install a mailbox post in the ground: step by step
- Call 811 a few business days ahead. The national call-before-you-dig line routes you to your state's center, and utilities mark their buried lines with paint or flags. Lead times vary by state. 811 does not mark private lines such as sprinklers or yard lighting.
- Pick the spot. Put the box where the carrier can reach it from the vehicle without getting out. Where your post office requires it, that means the right-hand side of the road in the carrier's direction of travel, even if your house is across the street; ask your carrier if you are unsure. Keep it clear of the driveway apron so it is not in the path of cars or plows.
- Measure the setback and mark the hole center. The 6 to 8 inch setback is measured to the mailbox door, not to the post. Since the post sits behind the door, mark the hole further back. Manufacturers give you the number for their own geometry: Mail Boss centers its in-ground post 16 to 18 inches from the street, and Whitehall's Balmoral instructions put the post center about 28 to 30 inches from the road because the box hangs on an arm.
- Dig the hole. USPS asks for no more than 24 inches of burial. Most residential posts need less: Mail Boss digs 12 inches below street level for its 43 inch in-ground steel post. Some manufacturer instructions differ from the USPS figure, for example Salsbury's in-ground post calls for a concrete footing about 12 by 18 inches that extends 24 inches or more, below the frost line. The 24 inch figure is a USPS maximum, not a minimum. Follow your post maker's instructions, and where they call for more than 24 inches, check with your local postmaster or road department first.
- Add gravel. Put about 6 inches of gravel in the bottom so water drains away from the end of the post. This matters most for wood, which rots where it sits in standing water.
- Set and brace the post. Stand the post in the hole, check the setback again, and brace it plumb on two faces with scrap boards. Now check the height: with the box resting on the post or bracket (or using its spec sheet), the bottom of the box or the point of mail entry must land at 41 to 45 inches above the road surface, not above your lawn. If the ground slopes down from the road, measure from the road level.
- Backfill with concrete or packed soil. Pour concrete evenly around the post, poking the mix with a stick to release air pockets, and slope the top so water runs off. If you want grass to the post, stop the concrete a few inches below grade and cover it with soil once it sets. If you are not using concrete, add soil in layers of a few inches and tamp each one hard. Recheck plumb as you go.
- Let it cure. Leave the braces on and wait the set time printed on your concrete bag before mounting the mailbox.
- Attach the mailbox. Use the manufacturer's bracket and bolts (see below), confirm the door opens fully toward the street, the flag works, and nothing blocks the slot.
- Add your house number. USPS asks for numerals at least 1 inch high in a contrasting color. If the box is on a different street from your home, add the full street address.
Worked example: the Mail Boss 43 inch in-ground post
People often ask how a 43 inch post can give a 41 to 45 inch mailbox. The answer is that the box adds height on top of the post, and Mail Boss measures to its mail slot, which sits high on the box.
- Post length: 43 inches. Hole: 12 inches below street level. Post top: about 31 inches above the street.
- Mail Boss says the incoming mail slot on the Mail Manager, Mail Boss and Package Master sits 11 to 13 inches above the mailbox floor.
- Result: 31 + 11 to 13 = a mail slot about 42 to 44 inches above the street, inside the USPS range.
If you need a deeper footing for frost or stability, Mail Boss suggests bolting a treated 4 x 4 inside the base of the steel post (it has predrilled holes) and burying the wood, so the steel post stays at the same height. Keep the total burial within 24 inches unless your postmaster says otherwise. Using a different box? Measure from its floor to its mail entry and redo the sum.
Concrete or gravel: how to set a mailbox post
Both work. The right choice depends on your soil, your climate and how likely the post is to be hit.
| Concrete footing | Gravel base and tamped soil | |
|---|---|---|
| Stiffness | Very solid; best for heavy locking boxes and loose or sandy soil | Solid if tamped well; can loosen over a few seasons |
| Replacement | You dig out the post and the concrete plug | Easy to pull and reset |
| Breakaway | Keep footings modest and within the 24 inch depth limit | Gives way more easily when struck |
| Rules | Whitehall notes some local Post Offices or county road commissions do not allow concrete backfill | Accepted almost everywhere |
| Typical use | Steel posts (Mail Boss sets its in-ground post in concrete), Salsbury pedestals | Wood 4 x 4 posts, sleeve-style posts |
Whichever you pick, put gravel under the post so water drains away from it.
In-ground vs. surface-mount posts
An in-ground post goes into soil. A surface-mount post bolts to a base plate that is anchored to existing concrete such as a curb, sidewalk or driveway edge. Use surface mount when there is no soil at the curb, or when you want to avoid digging altogether. Our no-dig mailbox post guide covers ground anchors as well.
How to install a surface-mount mailbox post
These steps follow Mail Boss's base plate instructions, which are typical for the category:
- Confirm placement and height with your local post office or carrier.
- Mark the concrete about 17 inches back from the street edge and center the base plate on the mark.
- Use the 8 holes in the Mail Boss base plate as a template and drill 8 holes with a masonry bit (or use self-tapping masonry screws).
- Anchor the plate with 8 masonry anchors; Mail Boss gives 1/4 inch x 3 inch outdoor masonry screws as typical.
- Bolt the post to the plate with the 4 mounting bolts supplied, check plumb and height, then mount the box.
The Mail Boss Surface Mount Post and Base Plate is built for a 4 to 8 inch sidewalk or curb, in 14 and 10 gauge galvanized steel with a powder-coated finish. Because the curb adds height, surface-mount posts are shorter than in-ground ones: a 27 inch post on a 4 inch curb puts the post top at about the same 31 inches as the in-ground post, and every extra inch of curb raises the mail slot by an inch. Our mailbox post buying guide shows how to work out the length.
How to attach a mailbox to the post
How the box goes on depends on the post type:
- Steel posts with a top plate (Mail Boss). The box bolts straight to the post. The Mail Boss steel post has prethreaded holes and ships with 4 mounting bolts. The Mail Manager PRO adds a Fast-Trak mounting plate to speed this up.
- Aluminum sleeve posts over a buried 4 x 4 (Whitehall). The decorative post slides over a treated 4 x 4, is fixed with lag bolts, and the bracket and mailbox floor bolt on with socket screws. Whitehall's Balmoral instructions also slip the plastic shipping sleeve over the buried wood as a moisture barrier.
- Polyethylene posts over a 4 x 4 (Mayne). Posts such as the Mayne Signature Plus install over a standard 4 x 4 wood post (not included) and carry the box on a support arm. Check the arm's minimum box width and weight limit: the Signature Plus is made for medium or large boxes at least 7 inches wide and under 16 lbs.
- Plain wood 4 x 4. Use a universal mounting plate or a 2 x 6 platform screwed to the top of the post, then fasten through the box floor with the screws supplied by the mailbox maker.
Before you tighten the last bolt, open the door: it should face the street, swing fully and leave the slot unobstructed.
Replacing an old mailbox and post
Unbolt the old box first and keep any reusable hardware. Dig around the old post and rock it free; soaking hard ground helps. A post set in concrete comes out with its plug attached, so dig wider and lever it up with a digging bar. Then reshape the hole, add fresh gravel and follow the steps above. The old spot is fine if it still meets the height and setback numbers.
Common mistakes to avoid
- Measuring the 41 to 45 inches from the lawn instead of the road surface.
- Measuring the setback to the post instead of to the door.
- Burying the post deeper than 24 inches or using a heavy rigid support that will not give way if hit.
- Skipping the gravel, which shortens the life of wood posts.
- Mounting the box before the concrete has set.
- Placing the post where plows push snow. Where snow removal is a problem, USPS suggests a semi-arch or extended-arm support, which lets the plow pass under the box.
Wondering whether to hire it out? Our mailbox installation cost guide breaks down DIY and pro pricing. Manufacturer instructions for the posts we sell are on each product page under "View all installation guides."
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Browse mailbox and post packages or post mount mailboxes for an existing post. Not sure which post fits your box or your curb? Contact us with a photo of your site and we will help you choose.
Frequently asked questions
How deep should a mailbox post be buried?
USPS says no more than 24 inches. Many posts need less: Mail Boss buries its 43 inch steel post 12 inches, leaving the top about 31 inches above the street. Follow your post maker; if it calls for more than 24, check with your postmaster.
How high should a mailbox be from the ground?
USPS asks for 41 to 45 inches from the road surface to the bottom of the box or the point of mail entry. Measure from the road, not your lawn, and ask your local postmaster if your street has no curb.
Do I need concrete to install a mailbox post?
Not always. Wood 4 x 4 posts can be set on gravel with tamped soil, and a no-dig ground anchor skips the hole entirely. Steel posts like the Mail Boss in-ground post are designed to be set in concrete.
How far from the curb should a mailbox be?
The mailbox door should be 6 to 8 inches back from the front face of the curb or road edge. The post itself sits further back, so measure to the door. Without a raised curb, your local postmaster sets the distance.
How long should concrete set before I attach the mailbox?
Follow the set time on your concrete bag and keep the post braced until then. Fast-setting mixes firm up sooner than standard mixes. Mail Boss says to wait until the concrete has set well before mounting the box.
Do I need to call 811 to install a mailbox post?
Yes. Contact 811 a few business days before digging, even for one post hole. Utilities will mark buried lines for you. Lead times vary by state, and private lines such as sprinklers are not marked.
******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******
