Fence Calculator: Posts, Rails, Pickets and Concrete
Sections are the run divided by the spacing, posts are sections plus one, and the concrete is the hole volume less the post. The number people miss is the plus one, and then again at every corner and gate.
When the figures look right, the fence material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- Total fence length150 ft
- Post spacing8 ft
- Rails per section3
- Picket width, 0 for panels5.5 in
- Gap between pickets0 in
- Post hole depth30 in
- Post hole diameter10 in
Posts needed20 posts
| Sections | 19 |
|---|---|
| Posts, plus one per corner and gate | 20 |
| Rails | 57 |
| Pickets | 328 |
| Concrete per hole | 1.15 cu ft |
| 50 lb concrete bags, whole job | 80 |
The material list this produces
| Posts | 20 |
|---|---|
| Rails | 57 |
| Pickets | 328 |
| Concrete, 50 lb bags | 80 |
What this calculator assumes
- Sections are the length divided by the spacing, and posts are sections plus one. Corners and gates each add a post on top of that.
- Concrete per hole is the hole volume less the post, figured at a 4x4. Two 50 lb bags per hole is the common shortcut and it is close.
- Set posts a third of their length in the ground in frost country, and check your local frost depth before you dig.
Count the posts twice
A straight 80 foot run at 8 foot spacing is 10 sections and 11 posts. Add a post at every corner and one on each side of every gate, since a gate post carries a swinging load and cannot double as a line post on both sides.
Gate posts are also usually bigger and set deeper than line posts. A 4x4 line post and a 6x6 gate post is a common combination, and a sagging gate a year later is almost always a gate post that was set like a line post.
Concrete per hole
A hole 10 inches across and 30 inches deep is 1.36 cubic feet. A 4x4 post occupies 0.26 of that, leaving about 1.1 cubic feet of concrete. A 50 lb bag yields around 0.375 cubic feet, so three bags per hole, not the two everyone quotes.
Set posts about one third of their above ground height into the ground, and never above the frost line in cold country. A 6 foot fence wants a 2 to 3 foot hole, and your local frost depth may demand more.
Pickets and the gap
Pickets butted tight at 5.5 inches wide need 2.18 per linear foot. Space them at half an inch and the coverage becomes 6 inches, which is 2 per foot, an 8 percent saving on picket count across the job.
Pressure treated pickets shrink after install, so tight butted today is gapped in six months. If the customer wants privacy, either buy kiln dried or overlap with a board on board layout, which costs about a third more in material.
Questions people ask
How many bags of concrete per fence post?
For a 10 inch hole 30 inches deep around a 4x4, about three 50 lb bags, or two 80 lb bags. The common advice of two 50 lb bags is short unless the hole is small.
How deep should fence posts be?
A third of the above ground height is the rule of thumb, so 2 feet for a 6 foot fence, and always below the local frost line. Gate and corner posts go deeper.
How far apart should fence posts be?
Eight feet on center is standard and matches common rail lengths. Six feet gives a stiffer fence on windy sites or with heavy privacy panels.
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Common sizes, worked out
The same calculator with the numbers already filled in, one page per size, each ending in its own material list.