Fence Post Depth Calculator — How Deep to Bury Posts
Enter your fence height and local frost line depth to find the recommended post burial depth — the calculator takes the maximum of the 1/3 rule, frost line and a 0.45 m minimum, then calculates total post length and concrete bags per hole.
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Maximum of: fence height ÷ 3, frost line depth, and 0.45 m code minimum
- 1
Structural (1/3) rule depth
1.8 ÷ 3 = 0.6 - 2
Frost line depth
0.6Posts must extend below the frost line to prevent frost heave. - 3
Recommended burial depth
max(0.6, 0.6, 0.45) = 0.60
How does this calculator work?
Post depth = max(fence height ÷ 3, frost line depth, 0.45 m). Total post to buy = fence height + depth. Concrete per hole = π × (holeDiameter/2)² × depth m³ — divide by 0.012 and round up for 25 kg bags. Multiply by post count for the project total.
Formula
How this is calculated
The depth a fence post must be buried is governed by three separate rules, and the largest of the three is used: (1) the structural 1/3 rule — depth should be at least one-third of the visible fence height so the post resists lateral wind and impact without tipping; (2) the frost line — in climates where the ground freezes, the footing must extend below the frost depth to prevent frost heave pushing the post upward each winter; (3) a code minimum of 0.45 m (18 inches), which is required in most jurisdictions even in warm climates. The total post length to purchase is therefore fence height plus that burial depth.
Concrete volume per hole is the cylinder formula: π × (hole radius)² × depth. A hole diameter roughly three times the post width gives enough concrete bearing area. One standard 25 kg pre-mix bag yields approximately 0.012 m³ of wet concrete; dividing hole volume by that yield and rounding up gives bags per post. Multiply by the total post count for the project total.
Frost line depth varies widely: effectively 0 in tropical and subtropical climates, 0.3–0.5 m in mild temperate regions, 0.6–1.0 m in central Europe and the northern US, and up to 1.5–2.5 m in continental or sub-arctic climates. Your local building authority publishes the design frost depth for the area; use that value for a code-compliant result.
Frequently asked questions
The rule states that the buried length should be at least one-third of the fence height above ground. This gives the soil enough resistance to lateral forces — wind, impact, frost — to keep the post upright. Gate posts and corner posts, which carry higher loads, are sometimes specified at 40% of fence height.
Not in tropical or subtropical climates where the ground never freezes. In those regions the structural 1/3 rule and the 0.45 m minimum govern. Enter 0 as the frost line depth and the calculator simply uses whichever of the other two rules is larger.
Concrete is strongly recommended for gate posts, corner posts, and any post over 1.5 m. For intermediate posts in well-draining sandy or gravelly soil, tamped gravel backfill is sometimes acceptable, but concrete gives better long-term performance in all soil types.
Also known as
TG we-Calculate Editorial Team. (2026). Fence Post Depth Calculator — How Deep to Bury Posts [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/fence-post-depth-calculator
TG we-Calculate Editorial Team. "Fence Post Depth Calculator — How Deep to Bury Posts." TG we-Calculate. 2026. https://we-calculate.com/calculator/fence-post-depth-calculator.
TG we-Calculate Editorial Team, "Fence Post Depth Calculator — How Deep to Bury Posts," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/fence-post-depth-calculator
@misc{wecalculate_fence_post_depth_calculator, title = {Fence Post Depth Calculator — How Deep to Bury Posts}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/fence-post-depth-calculator}}, year = {2026}, note = {TG we-Calculate} }
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