Mailbox Post Height Requirements
Install a mailbox at the wrong height and the USPS can withhold your delivery. This free mailbox post calculator applies the official mailbox post height requirements — the mailbox floor 41–45 inches above the road surface, the door 6–8 inches back from the curb — and tells you exactly how long your post must be, which standard lumber length to buy, and whether your planned placement passes both USPS rules.
Your installation
Your results
| How it's calculated | — |
|---|---|
| Buy this lumber length | — |
| 41–45 in. height rule | — |
| 6–8 in. setback rule | — |
Assumes a 4 in. mounting allowance so the box can be attached to the post top. USPS requires contacting your local post office before installing.
How to use this calculator
Measure four things at your install spot, all in inches: 1) how much higher (or lower) the ground is where the post will sit compared with the road surface — enter 0 if it's level; 2) how deep you'll bury the post (24 in. is the usual guideline for a 4×4); 3) your target mailbox floor height above the road — 43 in. is the safe midpoint of the USPS 41–45 in. range; and 4) the setback from the curb face to the mailbox door — 7 in. is the midpoint of the USPS 6–8 in. range. Results update instantly as you type, and the compliance checks turn red-free or flag problems the moment a value drifts outside the USPS windows.
How it works
USPS measures mailbox height from the road surface, not from your lawn. The official rule: the bottom (floor) of the mailbox — or the lowest edge of mail entry on locked designs — must sit 41–45 inches above the road surface, and the mailbox door must be set back 6–8 inches from the front face of the curb (or road edge where there's no curb). For the post itself, a 4×4 wooden post should be buried about 24 inches — deep enough to stay plumb and stable, shallow enough to break away safely if struck by a vehicle.
The post length formula is: (mailbox floor height − ground-vs-road difference) + burial depth + 4 in. mounting allowance. The first term is the above-ground portion of the post; the mounting allowance assumes you attach the box to the top of the post with a bracket or arm, which needs a few inches of post above the box floor. Example with the defaults: (43 − 0) + 24 + 4 = 71 inches, so you buy a 6-ft (72 in.) post.
The calculator snaps the required length up to the nearest standard lumber length (4, 5, 6, 8, or 10 ft) — lumber is sold in fixed sizes, so you always buy the next size up, never down. It also checks your floor height and setback against the USPS windows and tells you plainly whether each passes. One important caveat: these are the national USPS rules, but local ordinances and your postmaster can add requirements, so confirm placement and height with your local post office before you dig — USPS requires it.
Frequently asked questions
What are the USPS mailbox height requirements?
The bottom (floor) of the mailbox — or the point of mail entry on locked designs — must be 41 to 45 inches above the road surface. The measurement is taken from the road itself, not from the surrounding ground, so a box on a raised lawn needs a shorter post than one at road level. Contact your local post office before installing to confirm the correct placement and height.
How deep should a mailbox post be buried?
For a standard 4x4 wooden post, a burial depth of about 24 inches is the common guideline — enough for a stable, upright post while keeping the support breakaway-safe if a vehicle strikes it. Avoid rigid installations such as deep concrete footings, which can turn a post into a hazard. In very soft or sandy soil, go a little deeper and tamp the fill in layers.
How far should a mailbox be from the curb?
The mailbox door must be set back 6 to 8 inches from the front face of the curb — or from the road edge if there is no curb. That keeps the box clear of passing vehicles and snowplows while staying within easy reach of the carrier from the delivery vehicle. Install the box on the right-hand side in the carrier's direction of travel.
Do I need USPS approval for my mailbox?
Manufactured curbside mailboxes should carry the Postmaster General's (PMG) seal of approval. If you build a custom mailbox, you must show the plans to your postmaster and get approval before installing it. Either way, the USPS requires you to contact your local post office before installation to confirm the correct placement and height for your street.