Mailbox Post Calculator
USPS mailbox height, setback, and post compliance check.
What it does
Carriers pass hundreds of boxes a route, and reachable ones keep mail moving. Too low means bending at every stop, too far back means leaning from the truck. USPS dimensions fix both with three numbers.
The tool above checks floor height, setback, and bury depth. A 43 in floor set 7 in back on 24 in of post passes all three, needing a 67 in post from a 6 ft stock stick. The metric match is 109 cm with 18 cm back toward a 169 cm post.
Wood 4x4 or 2 in pipe with 24 in or less of bury keeps supports breakaway friendly. Concrete footings, milk cans, and masonry pillars turn minor clips into major damage, which roadside guidance warns against.
Call 811 before digging and the post office before mounting. Buried lines hide everywhere, and carriers confirm the exact door side and approach for the route.
How to use
- Pick imperial (in) or metric (cm).
- Enter floor height: 43 in or 109 cm.
- Enter setback: 7 in or 18 cm.
- Enter bury depth.
- Read post length and buy size.
- Confirm compliance before digging.
Formula
- floor
- Box floor height above road.
- setback
- Door face behind curb or edge.
- bury
- Post depth in soil.
USPS install rules set the box floor 41 to 45 in above the road surface with the door 6 to 8 in from the curb, on 4x4 wood or 2 in pipe buried 24 in or less. Roadside guidance favors lightweight breakaway supports over masonry. Post length adds floor to bury and rounds up to stock sizes.
Worked example
Example: 43 in floor, 7 in back
Imperial defaults: 43 in floor, 7 in setback, 24 in bury. These are also the default values, so the page opens on this answer.
- Floor: 43 in above the road.
- Setback: 7 in behind the curb.
- Bury: 24 in deep.
- Height check: 41 <= 43 <= 45 passes.
- Setback check: 6 <= 7 <= 8 passes.
- Bury check: 24 <= 24 passes.
- Post: 43 + 24 = 67 in, so buy a 6 ft post.
- Tool shows 67 in post (buy 6 ft post) with Compliant and 24 in deep.
- Metric match: 109 cm with 18 cm back gives a 169 cm post.
Reference table
| Floor | Setback | Post |
|---|---|---|
| 41 in | 6 in | 65 in, 6 ft |
| 43 in | 7 in | 67 in, 6 ft |
| 45 in | 8 in | 69 in, 6 ft |
Limits
- USPS curbside rules; wall slots differ.
- Ignores snow plow exposure by town.
- No utility locate included.
- HOA rules may add limits.
Common mistakes
- Mounting below 41 in.
- Setting past 8 in back.
- Concreting the post solid.
- Building masonry pillars.
- Skipping the carrier check.
Try it yourself
Quick checks. Answers sit tucked under each question.
41 in floor, 6 in back, 24 bury?
65 in post (buy 6 ft post) with Compliant and 24 in deep.
45 in floor, 8 in back, 24 bury?
69 in post (buy 6 ft post) with Compliant and 24 in deep.
Questions
USPS placement rule?
Mount the floor 41 to 45 in above the road with the door 6 to 8 in behind the curb.
Post length for the example?
Add floor height to bury depth. Here 43 + 24 = 67 in, so buy 6 ft.
Post type and bury?
4x4 wood or 2 in pipe, buried 24 in or less with no concrete or milk cans.
Brick pillar instead?
Lightweight breakaway supports beat masonry pillars that endanger drivers.
Carrier approval needed?
Ask the carrier first; local routes grant small exceptions.
Metric version?
Yes: 109 cm floor with 18 cm setback converts inside the same bands.