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Mailbox Post Calculator

Estimate total mailbox-post length from desired above-ground height and burial depth.

Updated April 18, 2026
Free online tool
Planning and research use

Why this page exists

Mailbox-post planning gets easier when the visible post height and burial depth are combined into one buy-length estimate instead of being guessed at the store. This calculator helps visitors estimate mailbox-post length from desired above-ground height and burial depth so it is easier to choose the right stock length before digging.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Mailbox post calculator

Estimate total mailbox-post length needed from above-ground height and burial depth.

Result

5.50 ft

Estimated mailbox-post length by adding desired above-ground height and burial depth.

Total post length needed5.50 ft

Above-ground height used3.50 ft

Burial depth used2.00 ft

Extra length above 4 ft standard stock1.50 ft

3.50 feet above ground plus 2.00 feet below grade points to about 5.50 feet of total post length.
This is useful for turning a visible mailbox height target into a practical post length before buying materials.
Use the result as a planning estimate only, because local mailbox rules and frost-depth needs can still change the final post length.

This is a simple length estimate only. Actual mailbox rules, local setbacks, frost depth, and post size requirements can affect the final post length you should buy.

Planning note

Last updated April 18, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Enter the above-ground mailbox-post height you want and the burial depth below grade.

The calculator adds the two lengths together.

It shows the total post length needed along with the above-ground and below-ground portions used.

Understanding your result

This is a simple post-length estimate only. Mailbox placement rules, frost depth, footing choices, and local roadway standards can still affect the final post length you should use.

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Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Choose the right post length before buying materials

A total-length result can help avoid buying a post that is too short once burial depth is included.

Compare standard depth with deeper frost-depth installation

Changing burial depth makes it easier to see how local soil or frost requirements affect the post length needed.

When to use it

Good times to run this calculator

Use this when you know how high the mailbox should sit above grade and want a quick total post-length estimate.

It is especially useful before buying pressure-treated or decorative post stock so burial depth is not forgotten.

Assumptions and limitations

The estimate assumes one simple above-ground height plus one burial depth describe the post correctly.

It does not model brackets, post caps, sloped terrain, special sleeves, or code-specific installation requirements.

Common mistakes

Avoid the usual input mistakes

Buying a post based only on the visible height can leave the installed post too short once burial depth is included.

Using a general burial assumption without checking frost or local mailbox rules can lead to a post that needs to be reset later.

Practical tips

Check the finished mailbox height requirement before buying the post so the above-ground assumption is based on the real target.

Review the estimate with post-hole concrete and gravel tools if you are planning the full footing and drainage setup at the same time.

Worked example

Walk through a realistic scenario

A worked example shows how the estimate behaves when the inputs resemble a real planning decision.

Estimate a mailbox post before purchase

A homeowner wants to buy one post length that will still work after burial depth is added for a stable installation.

1. Enter the desired above-ground height and burial depth.

2. Add the two numbers to estimate the total post length needed.

3. Compare the result with standard stock lengths before purchase.

Takeaway: The estimate is most useful because it turns a visible mailbox height goal into a practical buy-length decision.

FAQ

Common questions

How is mailbox-post length estimated here?

The calculator adds the desired above-ground post height to the burial depth entered to estimate the total post length needed.

Why can the needed length be longer than expected?

Because the buried portion often takes a meaningful share of the total post, especially where deeper setting or frost protection is needed.

Will this match local mailbox rules automatically?

No. Local roadway rules and postal guidance can affect final height, setback, and installation details, so the estimate should be checked against local requirements.

Related tools

Keep comparing

Post-hole concrete, fence-post, post-hole-gravel, and concrete tools help connect the post-length estimate to the full installation workflow.

Gravel and fence-cost tools add context when the mailbox post is part of a broader site-improvement project instead of a stand-alone replacement.

Home ToolsUpdated April 17, 2026