Fence Calculator

Size a fence run into posts, rails, pickets and concrete, using real board widths.

Your fence

The run

Add up every side you are fencing and enter the total. Corners do not need anything special here. A corner is simply a post that two sections meet at.
Eight feet is standard and matches the length rails are sold in. Drop to six on exposed sites or for heavy privacy panels, which catch a great deal of wind.

How it is built

Two rails suit a fence up to about four feet. Six feet of privacy fence wants three, and a fourth is worth it if the pickets are heavy or the boards are horizontal.
Two bags fills a typical ten inch hole around a 4x4. A six foot privacy fence, or anything in soft ground, wants a wider hole and three.
Use the real width, not the nominal one. A board sold as a 1x6 measures 5.5 inches, and a 1x4 measures 3.5. Assuming the nominal size leaves you short by roughly one board in twelve.
A privacy fence is butted tight, so this is zero. A picket or spaced fence typically leaves two to three inches, which cuts the board count noticeably.
Applied to the pickets only, since those are the parts you sort through and reject. Pressure treated stock straight off the pile is worth a full ten percent. 10.00%
Prices
Posts are the expensive part. Buy them long enough to sink a third of the finished height into the ground.
Priced per length, normally cut to match the post spacing.
The smallest unit price but the largest count, so a few cents here moves the total more than anything else on the list.
Posts to set
14 posts
Rails 39 rails
Pickets 240 boards
Concrete 28 bags
Sections
13 sections
Real post spacing
7.69 ft

What it costs

Material cost $1,425
Cost per foot $14.25

Every figure here is a planning estimate, not a professional takeoff. Yields, waste factors and code requirements vary by product, supplier and jurisdiction, so confirm quantities against the manufacturer’s data and your local building department before you order.

Generated by Mathterial

A fence is a parts list rather than an area, and each part is counted a different way. This fence calculator works out posts from the spacing, rails from the section count and pickets from the run, then adds the concrete for setting the posts.

Nominal sizes are not actual sizes

This is the error that shows up as a shortfall at the far end of the run, and it is entirely avoidable.

A picket sold as a 1x6 measures 5.5 inches, not 6. On a 100 foot run laid solid, the real width needs 240 pickets where the nominal figure suggests 220. That is 20 boards short, roughly 9%, and you find out at the end. The dressed sizes are not a supplier quirk: the American Softwood Lumber Standard, PS 20, puts a nominal 1x6 at 3/4 by 5 1/2 inches.

Measure a board rather than trusting the label. The same applies to the 4x4 that is really 3.5 inches, which matters when you work out the concrete.

Runs rarely divide evenly

Post spacing is a target, not a promise. A 100 foot run at 8 foot nominal spacing gives 13 sections, so the real spacing is 7.69 feet and the fence needs 14 posts, one more than sections because both ends are closed.

If the run is yours to set, pick a length that divides. At 96 feet or 104 feet the same fence lands on exactly 8 foot bays, which means every section is identical, every rail is a stock length, and nothing has to be cut to fit a short closing bay. It costs nothing to choose and it saves a fiddly afternoon.

What the spacing and gap decide

  • Post spacing drives posts, rails and concrete together. That 100 foot run takes 18 posts at 6 foot spacing, 14 at 8 feet and 11 at 10 feet. Wider bays save posts and concrete but need stiffer rails, and 8 feet is the usual limit for a 6 foot privacy fence in wind.
  • Picket gap drives the picket count alone. Solid takes 240 pickets on that run, a 2 inch gap takes 176, and a 3 inch gap takes 156.
  • Rails per section follows the height. Two rails suit a fence up to about four feet, three for a six foot privacy fence, and a fourth is worth it with heavy or horizontal boards.

Concrete for the posts

This page uses a rule of thumb of two bags per post, which puts a 14 post run at 28 bags. It is a reasonable planning figure and it is not a calculation.

For the real number, the post hole concrete calculator works it out from the hole you are actually digging and subtracts the post. A 10 inch hole three feet deep with a 4x4 in it comes out nearer 2.6 bags, so on a wider or deeper hole the rule of thumb runs short. Use it to budget and the other page to order.

Before you dig

Call the national utility location service on 811 before any post hole goes in, and confirm your property line rather than assuming the existing fence marks it. Many jurisdictions also cap fence height and govern which side the finished face must show, so check locally before buying material.

For a raised structure rather than a boundary, the deck calculator handles decking, joists and footings the same way.

Fence calculator FAQ

How many posts do I need for a 100 foot fence?

Fourteen at 8 foot nominal spacing, because 100 feet divides into 13 sections and both ends are closed. The real spacing works out at 7.69 feet. A run of 96 or 104 feet would land on exact 8 foot bays instead.

How many pickets do I need for a 100 foot fence?

About 240 laid solid, because a picket sold as a 1x6 actually measures 5.5 inches. Using the nominal 6 inches would suggest 220 and leave you 20 boards short. A 2 inch gap between pickets brings it down to 176.

How far apart should fence posts be?

Six to eight feet for most fences, with 8 feet the usual maximum for a 6 foot privacy fence exposed to wind. On a 100 foot run that is the difference between 18 posts and 14, along with the rails and concrete that go with them.

How much concrete do I need per fence post?

Two bags per post is the common planning figure, so 28 bags for a 14 post run. Worked out properly from a 10 inch hole 3 feet deep with a 4x4 post, it is closer to 2.6 bags, so budget with the rule and order from the real hole size.