Fence Calculator

The short answer

A 100-foot run of fencing with 8-foot panels needs 12.5 panels, so 13. Posts go at 8-foot centres, plus extras for corners, ends and the gate — typically 15 to 17 posts in total. Rails run three per section, about 39 for the run, and concrete is commonly one to two bags per post depending on hole size and soil.

What it depends on

Panel width drives the count, and 6-foot panels need more of them than 8-foot panels for the same run. Terrain changes everything: a slope needs either stepped panels, which requires trimmed posts, or a racked layout that follows the grade. Post spacing must match the panel width or nothing lines up, and gate posts need to be heavier and better set than line posts.

Where this stops being useful

This is a material estimate. Fence height, setback from the property line, permit requirements, easements and any homeowners association rules are local matters, and boundary location should be confirmed before digging. Utility locations must be checked before any post hole is excavated. General information and planning only, not engineering, structural or code advice.

Post spacing is the number that decides how much material you need, and it is set by the panel width rather than by taste. Panels come in fixed widths — typically six feet — and posts sit at the joins, so a run of twenty feet needs four panels and three posts between them plus the two end posts. Setting posts too far apart makes the fence flex and eventually bow out of line; setting them closer costs more but holds better on uneven ground. Check whether your ground is level, because on a slope the spacing has to follow the contour.

A fence is a long job with a lot of repetition, and the same arithmetic error repeats along every panel. Running the calculation once for the whole run rather than panel by panel keeps the post spacing consistent, which is what makes a fence look straight.

Post depth matters as much as spacing. A six-foot fence normally has posts set at least twenty-four inches in the ground, and deeper if the soil is loose or frost is expected. Use a post hole digger rather than a spade — a hand-dug hole is narrower than the post and you will fight it the whole way down. Concrete is optional; in firm soil it does nothing useful and makes the post harder to adjust, so check the ground first. Finally, confirm whether the gate posts need to be heavier, because they carry the whole gate weight and the usual post is not strong enough.

A fence is counted in pieces rather than in area, because pickets, posts and rails are bought as separate items with their own spacing rules. The picket count comes from the fence line divided by the width of one picket plus one gap; the post count comes from the same line divided by the post spacing; and the rails run between the posts, so their quantity follows the number of bays. Gaps and spacing are where the design lives. Tight pickets with a small gap give privacy and a solid look but trap wind and need strong posts. Wider gaps let air through, which reduces wind load and lets more light in, but the fence sees through. Privacy usually calls for a gap of no more than half a picket width, while a decorative or boundary fence can be much more open. Posts carry the load, so their spacing matters more than it looks. A typical timber fence uses posts every eight feet, with deeper or concrete-set posts on exposed or heavy fences. Setting posts in concrete and below the frost line prevents the slow heave that eventually loosens a fence, and the concrete itself — typically a couple of bags per post — is a material cost that is easy to leave out of the estimate. This calculator gives pickets, posts, rail length and a concrete allowance from your dimensions and spacing. It assumes a straight line of even ground; slopes need shorter bays or stepped rails, and corners need bracing posts. Measure the actual line with a string rather than pacing it, and check local rules on fence height and setback before you dig.

This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.