Fence Calculator

A fence is a row of sections between posts, so the whole calculation hangs on one thing people get wrong: there is always one more post than there are sections. Ten sections need eleven posts, because the run has two ends.

Gates complicate that slightly. A gate opening is not a fence section — it needs its own hanging post and latch post, and the opening itself has to come out of the run before you divide by the post spacing. Otherwise you end up a post short and a panel over.

Everything else follows. Panels equal sections. Pickets are the fence run divided by the picket-plus-gap pitch. Concrete is bags per hole times holes, and the depth of those holes is the one figure that decides whether the fence is still standing in ten years.

1. Step 1 Take out the gates fence_run = total_length − (gates × gate_width)
2. Step 2 Sections sections = ceil(fence_run ÷ post_spacing)
3. Step 3 Posts posts = sections + 1 + gates One more than sections for the closing end, plus one extra per gate opening.
4. Step 4 Panels or pickets panels = sections pickets = ceil(fence_run × 12 ÷ (picket_width + gap))
5. Step 5 Concrete bags = posts × bags_per_post Two 50 lb bags per hole is typical for a 4×4 in a 10 in × 30 in hole.

Example: 100 ft of privacy fence with one 4 ft gate. The fence run is 96 ft, which at 8 ft spacing is 12 sections and 12 panels. Posts are 12 + 1 + 1 = 14, needing about 28 bags of concrete.

• Post spacing is measured on centre. Pre-built panels require posts set at exactly the panel width, so set each post from the last rather than digging every hole in advance.
• One extra post is added per gate, on the basis that a gate opening needs a hanging post and a latch post while sharing one with the adjacent run. Double drive gates and free-standing gates need more.
• Concrete is estimated at two 50 lb bags per post, which fills a hole roughly 10 inches across and 30 inches deep around a 4×4. Corner, end and gate posts should get more, and wider or deeper holes obviously need more again.
• Post depth guidance is a third of the above-ground height or below the local frost line, whichever is deeper. Frost depth varies enormously — from nothing in the far south to over 4 feet in the northern US and Scandinavia — and local code governs.
• Terrain is assumed flat and the run straight. Slopes require either stepped or racked panels, corners need their own posts, and both add material.
• Picket counts do not include the extra pickets a gate needs, and do not account for the pattern needing to end cleanly at a post.
• Rails, caps, gravel boards and fixings beyond the headline items are not included. Neither is the gate itself.
• Property boundaries, setback rules, height limits and neighbour notification requirements are all local and are not modelled. Check before you dig.