How many fence boards do I need?

The post count is where people go wrong

A fence is four counts, and only one of them is tricky. Sections are the run divided by your post spacing, rounded up. Rails are sections multiplied by rails per section — two for a short picket fence, three for anything six feet tall. Pickets are the run in inches divided by the picket width plus the gap.

Posts are where the arithmetic bites. A run of fence needs one more post than it has sections, because there is a post at each end. A 100 foot run at 8 foot spacing has 13 sections but 14 posts. Ordering 13 leaves you one short at the very end of the job.

That formula assumes a single straight run. Every corner, every change of direction and every gate adds a post beyond the count, and gates need heavier posts than line posts because they carry a swinging load. Add one post per corner and two per gate opening, then set the gate posts in more concrete than the rest.

On spacing: 8 feet uses fewer posts and less concrete, which is why it is common on quotes. 6 feet is noticeably stiffer and holds a straight line better over the years, especially on a tall privacy fence that catches wind. For post holes, plan on a third of the post length in the ground — an 8 foot post for a 6 foot fence, set 2 feet deep. Our concrete calculator will size the footings.

A worked example: a three-sided backyard

Most backyard fences are not one straight line. Say you are fencing three sides: 60 feet, 90 feet and 60 feet, with 8-foot spacing. Entered as a single 210-foot run, the calculator gives 27 sections and 28 posts. Measured side by side, though, the 60-foot sides each need 8 sections and 9 posts, and the 90-foot side needs 12 sections and 13 posts. That is 31 posts, minus the 2 corner posts that are shared, for 29 posts.

The difference comes from rounding: each side rounds up on its own, and each corner needs a post exactly at the corner. So for any fence with corners, run the calculator once per side, add the posts, and subtract one for every corner where two sides meet. Then add the gate posts.

The pickets do not change much with the layout. 210 feet of fence with 5.5-inch pickets and a quarter-inch gap is 2,520 inches ÷ 5.75 = 439 pickets, minus about 8 for a 4-foot gate if the gate is built separately.

Concrete per post

Each post is set in a hole about three times the post width across, and roughly a third as deep as the post is long.

An 80 lb bag of concrete mix yields about 0.6 cubic feet. For the 29 posts above in 10-inch holes 2 feet deep, plan on about 45 bags.

Mistakes that cost money

• Not calling 811 before you dig. In the US, calling 811 a few days ahead gets buried utility lines marked for free. Hitting a gas or power line is dangerous and expensive.
• Skipping the survey line. Building a few inches over the property line can mean taking the fence down. If you are not sure where the line is, check your plat or survey first.
• Using untreated posts in the ground. Posts set in soil or concrete need lumber rated for ground contact, or they rot at the base within a few years.
• Forgetting the gate. A gate needs two heavier posts, hinges, a latch, and pickets that are counted separately from the fence run.

What it costs

As a rough guide, the materials for a 6-foot pressure-treated pine privacy fence often come to $15 to $30 per linear foot in the US, with cedar and composite costing more. For the 210-foot example, that puts materials somewhere around $3,000 to $6,300. Lumber prices change often, so price your exact list of posts, rails, pickets and concrete at a local yard.