Formula
Sections are the length divided by the spacing, rounded up. Posts are that count plus one, so an 80 ft run at 8 ft is 10 sections and 11 posts. Rails are the rail count times the length. Sticks are that footage divided by the stock length, rounded up. Two rails on 8 ft stock is 20 sticks.
pickets = floor((usable inches + gap) / (picket + gap))
concrete = π × radius² × depth − post² × depth
Usable length is the run minus the gates. A gate hangs on the line posts and does not add one. An 8 inch hole, 24 inches deep, minus a 3.5 inch post, is 0.528 ft³. An 80 lb bag yields 0.60 ft³, so each post is one bag and 11 posts are 11 bags. Those yields are Quikrete Concrete Mix 1101, the same ones on the concrete calculator.
Worked examples
80 ft, 8 ft spacing, two rails, 5.5 in pickets, 0.5 in gap, no gate. 11 posts, 20 rail sticks, 160 pickets, 11 bags of the 80 lb mix.
One 4 ft gate on that run. Posts stay 11. Pickets cover 76 ft instead of 80.
The hole by itself. π × 4² × 24 / 1,728 = 0.698 ft³ of hole. The 3.5 inch post occupies 0.170 ft³. The difference is 0.528 ft³.
Reference
Quikrete Concrete Mix 1101, the same yields as the concrete page.
| Bag | Yield |
|---|---|
| 40 lb bag | 0.30 ft³ |
| 60 lb bag | 0.45 ft³ |
| 80 lb bag | 0.60 ft³ |
Questions
Does a gate add posts?
Not on this page. The posts come from the whole run, and the gate is assumed to hang on two of those posts. Pickets stop where the gate is. If your gate needs its own posts, add them yourself.
Which concrete bag?
The same Quikrete Concrete Mix yields as the concrete calculator: 0.30, 0.45, and 0.60 cubic feet. The hole is a cylinder minus the dressed post. A 4×4 is entered as 3.5 inches.
Why is the picket count 160?
Eighty feet is 960 inches. A 5.5 inch picket and a 0.5 inch gap is a 6 inch pitch. floor((960 + 0.5) / 6) is 160. A privacy fence with no gap is a different count. Change the gap.
Sources
- Quikrete Concrete Mix data sheet 1101: 40 lb → 0.30 cu ft, 60 lb → 0.45, 80 lb → 0.60. Shared with the concrete calculator.
- Hole volume is a cylinder. The post is subtracted as a square of the dressed size. A nominal 4×4 is 3.5 in.
- Picket count is floor((length in inches + gap) / (picket + gap)). The 0.5 in gap is a default, not a fence style.