How Many Fence Panels and Posts Do I Need?

Take the gates off the run, divide by the panel width, and add one post. The arithmetic, the off-by-one everyone hits, and what to check before digging.

Posts are always one more than panels

That's the off-by-one that catches everybody, and it's easiest to see with a single panel.

One panel needs a post at each end — two posts. Add a second panel and it shares one of those, so you're at three. A third takes you to four. The pattern never changes: posts = panels + 1.

Then each gate adds one more, because a gate also needs a post either side and only one of them is already there from the panel run.

Your details

Total fence length(ft)

Panel width(ft)

6 ft and 8 ft are the common widths.

Number of gates(gates)

Width of each gate(ft)

3-4 ft for a path, 10-12 for a drive.

Rails per panel(rails)

3 for a 6 ft fence, 2 for anything lower.

Result

Panels needed

Gates taken off the run first, then rounded up.

Posts neededOne at each end, one between each pair, and one more per gate.: 14
Rails neededOnly if you are building panels rather than buying them made up.: 36
Run to fill with panelsTotal length minus the gate openings.: 96
Width of the last panelThe offcut at the end. Equal to a full panel if the run divides evenly.: 8

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The arithmetic

A 100-foot fence with 8-foot panels and one 4-foot gate.

Take the gate off first. A gate opening is filled by the gate, not by panels:

100 − 4 = 96 feet to fill with panels

Divide by the panel width:

96 ÷ 8 = 12 panels

Posts — panels, plus one, plus one for the gate:

12 + 1 + 1 = 14 posts

Rails, if you're building panels rather than buying them made up. Three per panel on a 6-foot fence:

12 × 3 = 36 rails

And 14 posts means 14 holes to dig, which is the number that actually tells you how long your weekend is.

When the run doesn't divide evenly

It usually doesn't. A 100-foot run with 8-foot panels and no gate gives 12.5 panels — so you buy 13 and cut one down.

The calculator shows you how wide that last panel will be, which is worth knowing before you start, because a very narrow one looks like a mistake even when it isn't. If you'd end up with a 9-inch sliver at the end, it usually looks better to trim two or three panels slightly and spread the difference than to leave one obvious runt at one end.

Decide that before you set any posts. It's a five-minute decision at the planning stage and a full rebuild afterwards.

Corners

The calculator handles one straight run. A fence that turns needs a post at the corner itself.

The clean way to handle it is to treat each straight section as its own run, calculate each, and add them — remembering that the corner post gets counted by both runs, so subtract one for each corner you share.

Measure a real panel before you dig

The single most useful thing on this list.

Nominal panel widths aren't always exact, and they vary between suppliers and sometimes between batches. If you dig every post hole to the catalogue figure and the panels arrive an inch narrower, you're either forcing them in or packing gaps out — along the entire run.

Take one delivered panel, measure it on the ground, and set your spacing to that. One measurement saves the whole fence.

Check the boundary, not the old fence

Worth its own section because it's expensive to get wrong.

An existing fence is not proof of where the boundary is. Fences get replaced slightly off-line for decades, and the error compounds. Before you commit posts to concrete, confirm the actual boundary — and if the fence is shared, talk to your neighbour first. It's a much easier conversation before the posts are set than after.

Same for height restrictions and permits, which vary by area and are usually stricter at the front of a property than the back.

What this doesn't count

Concrete for the posts. That depends on hole size and post depth. Rule of thumb: the hole is about a third of the post height deep, and about three times the post width across.
Gravel at the bottom of each hole for drainage.
Post caps, gate hardware, hinges and a latch.
Slope. A fence running downhill is either stepped or raked, and both change the panel count from the flat-run answer.

Where people get it wrong

Posts = panels. The off-by-one at the top of this article. You'll be one post short, always at the end.
Not deducting the gate. A 4-foot gate opening filled with panels means one panel too many and a gate that doesn't fit.
Digging before checking services. Know what's under the line first.
Trusting the old fence line. See above.
Setting spacing from the catalogue. Measure a real panel.
Forgetting which way the gate opens. Decide the swing before the hinge posts go in.

The short version

Take the gate widths off the total run, divide what's left by the panel width and round up — that's your panels. Posts are panels + gates + 1. Add one post per corner. Measure a real panel before you dig, confirm the boundary before you concrete anything, and remember every post is a hole.