Mailbox Post Replacement: USPS Regulations, Post Materials, and Setting Depth

USPS Requirements

The bottom of the mailbox must be 41 to 45 inches above the road surface. This is the height that allows a mail carrier to reach the box from their vehicle without getting out. Measure from the road surface, not the ground level at the post — these are often different if the shoulder slopes.

The front face of the mailbox must be 6 to 8 inches back from the curb edge. In rural areas without curbs, 6 to 8 inches from the road edge. This prevents the box from being clipped by passing vehicles while keeping it within arm's reach of the mail truck.

The mailbox door must face the street and open toward approaching traffic (the mail carrier's vehicle). For most suburban streets in the US, this means the door faces the street on the right-hand side of the road.

USPS requires that mailbox posts be breakaway or yield on impact. This means no massive brick or stone structures that could injure a driver in a collision. A standard 4x4 wood post buried 24 inches deep meets this requirement. A steel post set in concrete does not — it becomes a rigid obstacle.

Post Material Options

Pressure-treated 4x4 posts are the standard choice. A 6-foot post (24 inches underground, 42 inches above grade, plus room for the mailbox mounting board) costs $8 to $15. They last 10 to 15 years in the ground before rot sets in at the soil line.

Cedar 4x4 posts resist rot naturally and look better but cost more ($15 to $30). They last about as long as pressure-treated in most climates.

Pre-made mailbox post assemblies from home centers include the post, a decorative top, a cross arm for the mailbox, and sometimes a newspaper holder. They cost $30 to $80 and save design time, but the decorative elements are often thin wood or plastic that weathers poorly.

Composite and PVC mailbox posts resist rot completely and never need painting. They cost $60 to $150 but last indefinitely. If you are tired of replacing a rotted wood post every decade, composite is the long-term answer.

Removing the Old Post

If the old post is set in concrete, dig around the concrete footer with a shovel to expose it. Rock the post back and forth to loosen the concrete from the surrounding soil. Use a pry bar or a car jack under a board as a lever to pull the concrete footer out of the ground.

For a stubborn concrete footer, dig around it, wrap a chain around the post above the concrete, and pull with a vehicle. Or break the concrete apart with a sledgehammer. The concrete usually comes out in one piece if you dig enough clearance around it.

If the old post is simply rotted at the soil line and the underground portion is gone, dig out the remaining stump pieces and the old concrete. Start with a clean hole.

Setting the New Post

Dig the hole 24 inches deep and about 12 inches in diameter. A post hole digger handles this size hole easily. If you hit large rocks, a digging bar or breaker bar helps.

Set the post in the hole and check for plumb on two adjacent faces with a level. Brace the post plumb with scrap lumber nailed to stakes in the ground.

Pour fast-setting concrete (Quikrete) into the hole around the post. Add water per the bag instructions. Most fast-setting mixes harden in 20 to 40 minutes. Mound the concrete slightly above grade and slope it away from the post so water drains away from the base.

Let the concrete cure for 4 hours before mounting the mailbox. Full strength takes 24 to 48 hours, but the post will be stable enough for the mailbox weight after a few hours.

The mailbox mounts to the post with screws through the bottom of the mailbox into the post or a mounting board. Use stainless steel or galvanized screws — plain steel rusts and stains the mailbox.

Frequently Asked Questions