Calculate structural fence post hole depth, hole diameter, total post lumber length, frost line penetration, gravel drainage base, and concrete bags per post.
Post Embedment: 30" + Gravel Bed: 6"
When water in the subsoil freezes, it expands with immense hydraulic pressure. If a concrete footing is poured shallowly above the seasonal freeze line, freezing groundwater gets beneath the flat concrete bottom and lifts the entire post upward. Our calculator automatically enforces local frost line penetration plus a 6-inch safety extension to guarantee frost stability.
A solid 6-foot wooden or vinyl privacy fence functions exactly like a nautical sail under wind storms, exerting massive lateral overturning moments at ground level. Applying the one-third to one-half depth rule ensures sufficient counteractive passive soil resistance to keep posts plumb without leaning or blowing over.
Enclosing the bottom of a wooden post completely in concrete forms an impervious bowl that traps subterranean rainwater against the porous end grain of the timber, rotting pressure-treated lumber in under 5 years. Factoring a 4 to 6-inch crushed stone gravel bed allows water to percolate away from the bottom cut.
Under-ordering concrete results in incomplete footings that weaken over curing pauses, while over-ordering leaves bulky 50-lb sacks to ruin in the rain. We subtract the exact physical displacement volume of the buried post timber from the excavated cylinder hole to provide precise bag counts for 50-lb, 60-lb, or 80-lb mixes.
| Fence Height | Post Dimension | Hole Diameter | Standard Embedment | Gravel Base | Order Lumber | 50-lb Bags |
|---|---|---|---|---|---|---|
| 4 ft (Picket / Garden) | 4" × 4" Timber | 10 inches | 24 inches (2.0 ft) | 4 inches | 6.5 ft or 8 ft | 2 to 2.5 Bags |
| 6 ft (Line Privacy) | 4" × 4" Timber | 12 inches | 30 to 36 inches | 6 inches | 8 ft or 9 ft | 3 to 3.5 Bags |
| 6 ft (Corner / Gate) | 6" × 6" Timber | 16 inches | 36 to 42 inches | 6 inches | 10 ft | 5 to 6 Bags |
| 8 ft (Commercial / Deer) | 4" × 4" / 6" × 6" | 12 to 16 inches | 42 to 48 inches | 6 inches | 12 ft | 4 to 6 Bags |
Enter the planned finished height of your fence panels above ground level (typically 4', 6', or 8').
Select standard intermediate line post, privacy corner post, or heavy swinging gate hinge post.
Enter your local building department's official frost line depth to ensure the footing reaches 6" below freeze level.
Add 4 to 6 inches of crushed stone gravel bedding at the excavation base for timber moisture drainage.
Inspect total dig depth, recommended timber lumber purchase length (8', 9', 10', or 12'), and 50-lb concrete bags.
Calculates exact depths using both the 1/3 post height formula and the 1/2 wind-resistance multiplier.
Enforces an automatic 6-inch footing extension below winter freeze depths up to 72 inches.
Accurately subtracts submerged post volume from concrete calculations, saving you up to 25% on concrete costs.
Dynamic vector schematic updates in real-time showing timber embedment, frost depth, concrete collar, and gravel base.
