Fence Post & Material Calculator

Fence posts mark the boundaries between sections, not the sections themselves. A 100 ft fence divided into 13 sections needs a post at the start of each section plusone final post at the far end — that end-cap post is the “plus one.” Without it, the last section has no closing post to attach rails and pickets.

The formula is straightforward: divide total fence length by your target post spacing and round up to get the number of sections. Then add one for the closing end post. Actual spacing is then recalculated by dividing total length by the section count so every bay fits the run evenly.

Worked example: A 100 ft fence with 8 ft target spacing yields CEILING(100 ÷ 8) = 13 sections and 13 + 1 = 14 posts. Actual section spacing becomes 100 ÷ 13 ≈ 7.69 ft — slightly tighter than the 8 ft target, but every bay is identical and the run closes cleanly at both ends.

Post hole depth determines how well your fence resists frost heave and wind load. A common rule of thumb is to set the buried portion of the post to one-third to one-half of the total above-ground post height. A 6 ft fence on a 4×4 post typically needs 24–36 inches below grade, depending on soil type and exposure.

In northern climates, local building codes specify a minimum depth to the frost line— the depth at which soil stops freezing in winter. Frost heave can push shallow posts upward over several freeze-thaw cycles, leaving rails and pickets misaligned. Check your jurisdiction's frost depth map before setting posts; depths of 36–48 inches are common in cold regions, while southern climates may allow 18–24 inches.

Wind exposure also matters. Tall privacy fences on open lots catch more lateral force than short picket fences in sheltered yards. Deeper holes, wider footings, and concrete collars around the post base improve resistance. This calculator estimates concrete bag count per hole — adjust the bags-per-post input if your local code or engineer specifies a larger footing volume.