Fence Post Depth Calculator
Find the recommended hole depth for setting fence posts, plus an optional frost-line check for cold climates.
Total post length to buy
How recommended post depth is calculated
The baseline rule for setting any fence post is to embed roughly one-third of its total above-ground height into the ground. A typical 6-foot post gets about 24 inches of embedment under this rule, which is the standard depth guidance in wood fence construction references.
Where the ground freezes seasonally, a second rule can call for more depth: the base of the post hole should sit below the local frost line, since freeze-thaw cycles can slowly heave a post upward if it isn't anchored beneath that depth. When the frost line runs deeper than the one-third rule would require, code and best practice generally follow the frost depth instead.
This calculator takes the larger of the one-third rule and the frost depth entered as the recommended embedment, adds a gravel base for drainage, and adds hole depth back to above-ground height to get the total length of post material to buy.
Where these numbers come from
The formula and default values in this calculator are based on:
- One-third embedment rule of thumb is standard residential fence-post installation guidance found in wood fence construction references; frost-line-depth setting practice is the added standard for jurisdictions with seasonal ground freeze.
These are planning estimates. Check your local building code, product specifications, and a licensed contractor before you buy materials or build.
Frequently asked questions
Do I need to enter a frost line depth?
Only if your area gets seasonal ground freeze. In warm and mild climates without a frost line, the one-third-of-height rule sets the depth on its own -- leave that field at 0.
Do I always need to dig below the frost line?
Only where frost heave is a real concern for your climate and local code requires it -- this is common in northern climates with seasonal ground freezing. Check your local frost depth data or building department for the number to enter.
Why add a gravel base under the post?
A few inches of gravel below the post improves drainage under the post bottom, which helps keep the end grain of a wood post away from standing water and slows rot. It's a common recommendation in wood fence installation guides even where it isn't a strict code requirement.
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