How Deep Should a Mailbox Post Be?
Mailbox posts are usually set about two feet deep. The Postal Service sets the height and the distance from the curb but not the depth, and highway safety guidance favors posts that break away if a car hits them. This page covers depth, USPS placement, frost heave, and how to set a post without a dangerous concrete block.
- Checked October 2026
- 3 sources
- How we verify
- Mailbox height, USPS41 to 45 inFrom the road surface to the bottom of the box or the point of mail entry.
- Setback, USPS6 to 8 in from the curbFrom the curb face or road edge to the mailbox door.
- Breakaway limit, FHWA via USPS4x4 wood or 2 in pipeBuried no more than 24 in, so it should break away if struck.
What Depth Does a Mailbox Post Need?
A mailbox post is usually set about 2 feet (61 cm) deep. The Postal Service does not set a depth. Federal highway guidance, reproduced in a Postal Bulletin, says a wooden support no larger than 4 by 4 inches, or a 2 inch pipe, buried no more than 24 inches, should break away if a vehicle hits it.
So 24 inches is the upper end, not the target, for a post beside a road. Look up your frost line depth and check your local rules, because some towns set their own.
How High and How Far From the Road Should a Mailbox Be?
The Postal Service recommends a height of 41 to 45 inches from the road surface to the bottom of the mailbox, or the point of mail entry, and a setback of 6 to 8 inches from the front face of the curb or road edge to the mailbox door. Local conditions vary, so contact your local post office first.
| Item | USPS recommendation |
|---|---|
| Height | 41 to 45 in from the road surface to the bottom of the box or the point of mail entry |
| Setback | 6 to 8 in from the front face of the curb or road edge to the mailbox door |
| Snow areas | A semi-arch or extended-arm support lets plows sweep near or under the box |
Some places differ. One Texas city asks for at least 18 inches from the pavement edge, and one Idaho county asks for 8 feet. Where the Postal Service and the city disagree, the stricter rule applies.
Should a Mailbox Post Be Set in Concrete?
Beside a road, a mailbox post is often better not set in a concrete plug. Highway guidance favors a support that bends or breaks if a car hits it, and a heavy post in a big concrete block does not. Some local codes say a support shall not be set in concrete unless it is a designed breakaway system.
Where concrete is allowed, keep it small, and where your department allows a standard breakaway post, set it in compacted soil or gravel. The mailbox must also stay attached to the post, so it does not become a loose object in a collision.
Larger posts are allowed only under certain designs. One Texas city permits wood, steel or aluminum pipe posts up to a 6 inch nominal dimension when specifically designed as a breakaway system under AASHTO guidelines. Ask your public works department.
How Do You Stop a Mailbox Post From Heaving?
Set the post in free-draining gravel rather than a concrete plug, and bury it no deeper than the breakaway limit. Frost lifts what it can grip, and a smooth post in gravel gives it little to grip. A post set in concrete can be lifted by frozen soil that bonds to the plug.
Slope the soil away from the post so water runs off, and check the post each spring. Frost heave explains the conditions that lift posts.
Call 811 before you dig, as with any post hole.
Questions People Ask
How deep should a mailbox post be?
About 2 feet is common, and 24 inches is the upper limit in the FHWA guidance reproduced by the Postal Service for a post that should break away. Frost can lift a post set in concrete, so use gravel backfill and check local rules.
Should a mailbox post be set in concrete?
Often not, beside a road. FHWA and AASHTO guidance favors supports that break away, and some local codes bar concrete unless the support is designed as breakaway. Ask your public works department before pouring a plug.
How high should a mailbox be off the ground?
USPS recommends 41 to 45 inches from the road surface to the bottom of the mailbox or the point of mail entry, and 6 to 8 inches from the curb face to the mailbox door. Check with your local post office, because local conditions vary.
What Is Your Frost Line Depth?
Enter a ZIP code or city to see the depth your own building code sets.