How Many Fence Posts Do I Need?

The post count is the part people get wrong, and it is nearly always wrong in the same direction — one short, because the last post gets forgotten.

ConstructionBy Aug 26, 20266 min read
How Many Fence Posts Do I Need? — ListCalc

Sections plus one

Post counting trips people up because the intuitive answer is off by one. If you have five fence panels in a straight line, you need six posts — one at each end of the run plus the four shared between panels.

So the rule is: work out the sections, then add one post.

A worked run

Take 120 ft of fence with a single 4 ft gate, posts at 8 ft spacing.

The gate takes up 4 ft that does not need fencing, so the fenced length is 116 ft.

116 ÷ 8 = 14.5, which rounds up to 15 sections. The last one is short, and that is normal — you trim it rather than leaving a gap.

15 sections means 16 posts. Then add the extras: two corner or end posts and one extra post for the gate, which needs a post on both sides. That gives 19 posts.

Rails and pickets follow from the sections

Most fences use three rails per section — top, middle and bottom. At 15 sections that is 45 rails, or 360 linear feet of rail material.

Pickets depend on width and spacing. For 5.5 inch pickets butted tight across 116 ft, you need about 254, and it is worth ordering around 272 to allow for warped or split boards in the stack.

Depth, and why you buy taller posts than the fence

The standard guidance is to bury a third of the post's above-ground height, or go below the frost line, whichever is deeper. For a 6 ft fence that means about 2 ft in the ground — so you buy 8 ft posts and only 6 ft of each shows.

In cold climates the frost line rules. If it sits at 42 inches where you live, a 2 ft hole will heave the post out of plumb after the first hard winter, no matter how much concrete is in it.

Concrete adds up faster than expected

A 10 inch hole 30 inches deep takes roughly 1.1 cubic feet of concrete. An 80 lb bag of mix yields about 0.6 cubic feet, so that is close to two bags per post. At 19 posts you are looking at roughly 35 bags — about 1.4 tons of material, which is worth knowing before you decide how many trips the car is making.

Check the line before you dig

Mark every post position along the whole run and stand back before the first hole goes in. Corners and gate posts are the ones that have to be right, because everything else spaces off them. A post set 4 inches out of line is a five-minute fix before the concrete goes in and a weekend afterwards.

Run your own numbers

Fence Concrete Length

FAQ

How do I calculate the number of fence posts?
Divide the fenced length by your post spacing to get the number of sections, then add one. A 116 ft run at 8 ft spacing gives 15 sections and 16 posts, before you add corner and gate posts.
Why is it sections plus one?
Because posts sit at both ends of every section and neighbouring sections share a post. Five fence panels in a straight line need six posts, the same way five gaps between fingers need six fingers.
What spacing should I use between posts?
6 to 8 ft is standard. 8 ft is the most common because rails and pickets are sold in 8 ft lengths. Go to 6 ft for tall privacy fences or anywhere exposed to strong wind, where longer spans flex.
How deep should fence posts be set?
The usual guidance is a third of the post's above-ground height, or below the local frost line, whichever is deeper. A 6 ft fence typically means 2 ft in the ground, so you buy 8 ft posts.
How much concrete does each post need?
For a 10 inch diameter hole 30 inches deep, roughly 1.1 cubic feet per post, which is about two 80 lb bags. Multiply by your post count and add a bag or two spare.