Inputs
Recommended Embedment Depth
—
Below finished grade
Post Hole Depth (incl. gravel)
—
Hole depth = gravel base + embedment
Footing Diameter
—
Auto sized ≥ 3× post width with height factor
Concrete Volume
—
Cubic ft / bags 80 lb (≈0.6 ft³) and liters
Example Scenarios
Typical examples using average loam soil and medium wind exposure.
| Fence Height | Frost Line | Soil | Wind | Embedment | Footing Ø | Concrete |
|---|
Formula Used
This estimator blends common field practice with simple multipliers:
- Rule of thumb: Embedment ≈ one-third of above-ground height (D₁ = 0.33 × H).
- Frost protection: Go at least to frost line; add 0.5 ft (15 cm) safety (D₂ = frost + 0.5 ft).
- Soil & wind multipliers: Apply a factor for weaker soils and higher wind exposure (M).
We compute Dbase = max(D₁, D₂). Then D = M × Dbase with caps so D ≤ H. Typical multipliers:
- Loose Sand: ×1.25
- Average Loam: ×1.00
- Dense Clay: ×1.15
- Gravelly / Well-Drained: ×0.95
- Wind Low: ×1.00
- Wind Medium: ×1.10
- Wind High: ×1.20
Footing diameter auto-sizes to the largest of: 3× post width, 0.25 × H (inches), and 9 in (230 mm), unless overridden. Concrete volume assumes a cylindrical hole filled to embedment depth. Bags: 80 lb ≈ 0.60 ft³; 50 lb ≈ 0.375 ft³.
This is a planning aid only. Local codes, frost data, wind maps, and soil conditions vary. When in doubt, consult local standards or a licensed professional.
How to Use This Calculator
- Select units and enter your fence height above grade.
- Enter the frost line for your location; use 0 if not applicable.
- Choose soil class, wind zone, and post size or set a custom diameter.
- Optionally override footing diameter; otherwise the tool auto-sizes. Set gravel base thickness.
- Press Calculate. Review embedment, hole depth, footing diameter, and concrete volume. Export results to CSV or PDF for your records.
FAQs
Where freezing occurs, posts should extend below the frost line to limit heave. This tool enforces at least frost line plus a small safety allowance.
It is a practical starting point that balances overturning resistance with material use. Real requirements depend on wind loading, panel permeability, soil, and local codes.
Belling increases bearing area and resistance in some soils. In wet soils, free-draining gravel around or below the post may help mitigate frost and water issues.
Solid panels and privacy fences catch more wind and may need deeper embedment or larger footings than open picket or wire fences. Increase depth when exposure is high.
Consult local building departments, state transportation manuals, or trusted maps published for your region. When uncertain, be conservative and add depth.
Notes & Tips
- Cap embedment so the buried length does not exceed fence height.
- Increase depth for gates, corner posts, or poor drainage.
- Taper or crown the top of concrete to shed water.
- Verify underground utilities before digging.