Fence Calculator
Posts are the expensive part and the part that fails first. This counts them from your run and spacing, then works out pickets, rails and the concrete each hole needs.
Fence material calculator
Pickets per foot by width and gap
| Picket and gap | Pickets per 100 ft | For your run |
|---|
Post depth and concrete by footing size
| Hole | Concrete per post | Bags of 50 lb |
|---|
Posts are the part that fails
A fence fails at the base of a post long before the pickets wear out. Posts carry the wind load for the whole panel, and a post set 24 inches deep in a 10 inch hole will lean within three seasons while the wood above it is still sound. The count here is driven by spacing plus the extra posts at gates, corners and ends of run — those carry more load than a line post and deserve a bigger hole.
At 8 foot spacing, a 100 foot run needs 13 bays and 14 posts. Two more go in at the gate, one on each side, which is why the total is 16. If the run turns a corner, add one more: a corner post is doing the work of two directions at once.
How the count is calculated
Posts are the run divided by spacing, rounded up to whole bays, plus one for the end, plus two per gate. Pickets are the run in inches divided by picket width plus gap. Rails are the number of bays times the number of rails each bay carries.
A 6 foot fence needs three rails per bay — top, bottom and middle — because a 5-1/2 inch picket spanning 8 feet with only two rails will cup and bow. A 4 foot fence takes two. That one line is the difference between 26 rails and 39 on this run.
Setting the posts
Depth is set by frost, not by preference. In the northern half of the US the footing has to go below the frost line — 36 to 48 inches — or the post will heave in the first hard freeze. In the South, 24 to 30 inches is common and adequate. Your building department publishes the number and it is worth the phone call.
Concrete quantity follows the hole, not the post. An 8 inch hole 36 inches deep takes about 1.3 cubic feet, which is roughly 1-1/2 bags of 50 pound mix. A 10 inch hole at the same depth takes 2 bags. The table below shows the range; the default here assumes 1.5 bags per post.
Pickets, gap and what the rules require
Picket count is pure arithmetic — 5-1/2 inch pickets with a 1/4 inch gap means 5.75 inches of run each, and 1,200 inches divides into 209 pickets. Changing the gap to 3/8 inch drops the count to 205, which matters because privacy and pool codes often regulate the gap more tightly than the height.
Many jurisdictions cap a residential fence at 6 feet in a rear yard and 4 feet in a front yard. Pool barriers are their own code: usually 4 feet minimum with gaps small enough that a 4 inch sphere will not pass, self-closing and self-latching gates, and no climbable horizontal rails on the outside face.
What this does not count
Gate hardware and the gate itself, which is a small framed panel and is usually bought as a kit. Post caps, which are cosmetic but keep water out of the end grain and roughly double post life. Stain or sealer. And the old fence, which has to be pulled and disposed of — often the largest single line in the job.
Frequently asked questions
How many posts do I need for 100 feet of fence?
Fourteen at 8 foot spacing, plus two for a gate, so sixteen. Add one more for each corner, because a corner post carries load from two directions.
How many pickets do I need for 100 feet of fence?
About 209 at 5-1/2 inches wide with a 1/4 inch gap. Wider pickets or a wider gap reduce the count slightly; narrower pickets or a tighter gap increase it.
How deep should fence posts be set?
Below the frost line, which is 36 to 48 inches across most of the northern US and 24 to 30 inches in the South. Local code sets the number and it is enforced at inspection.
How many bags of concrete per fence post?
One and a half bags of 50 pound mix for an 8 inch hole 36 inches deep, or two bags for a 10 inch hole. Set the post, pour, and slope the concrete away from the wood.
How many rails does a 6 foot fence need?
Three per bay — top, bottom and middle. A 4 foot fence takes two. Fewer rails on a tall panel lets the pickets cup and bow between posts.
Should I use concrete or gravel to set posts?
Concrete resists lateral load and is the standard for a fence. Gravel drains better and is easier to replace a post in, but a gravel-set post in wind is more likely to work loose.
Can I put a fence on a property line?
Usually it goes just inside the line, and many areas require a survey before you build. Check setback rules and any HOA covenant before digging, because a fence in the wrong place can be ordered removed.
Disclaimer: This calculator estimates posts, pickets, rails and concrete from your run and spacing. Actual quantities depend on grade changes, corner count, local frost depth and fence code, which this tool does not evaluate.
Citing this page? FigureMill, “Fence Calculator” (last reviewed October 31, 2026). Fence post, picket, rail and concrete quantities from run length, post spacing, picket width and gap. https://figuremill.com/materials/fence-calculator
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