The fence calculator turns your fence line into a post count and panel count — solid numbers for the shopping list. Whether those posts actually stay upright for the next twenty years comes down to depth, backfill, and spacing, none of which a materials calculator can decide for you.
The 1/3 Rule for Post Depth
A fence post should be buried at least a third of its total length. A 6-foot fence post, for example, wants roughly 2 feet in the ground. In colder climates, depth needs to go below the local frost line regardless of that ratio — frost heave (the ground freezing and expanding) can slowly push a shallow post out of alignment over a few winters, even if it looked perfectly set the day you installed it.
Concrete vs Tamped Gravel
Concrete footings are the stronger, more permanent option and the default most people reach for. Tamped gravel backfill (added and compacted in layers) is a legitimate alternative, and in wet or poorly-draining soil it can actually outlast concrete — gravel lets water drain away from the wood post, while concrete can trap moisture against it and accelerate rot at the base.
Keep Spacing Consistent
Your panel width should match the post spacing you enter into the calculator, exactly. Uneven spacing is the single most common reason a finished fence looks slightly "off" even when every post is perfectly plumb and level — the eye catches inconsistent rhythm faster than it catches a lean.
Run your own numbers with the fence calculator, keeping post spacing and panel width matched to your actual panels.