How the fence materials are calculated
A wood fence is a repeating pattern of sections. Each section spans from one post to the next, carries two or three horizontal rails, and is covered with pickets. Once you know how many sections fit along your fence line, everything else follows.
Sections = fence length ÷ post spacing (rounded up)
Posts = sections + 1 + one extra per gate
Rails = sections × 2 (or × 3 for fences 6 ft and taller)
Pickets = fence length (in) ÷ (picket width + gap)
Example: 150 feet of 6-foot privacy fence with posts every 8 feet has 19 sections, so you need 20 posts plus 1 for a gate (21 total), 57 rails, and about 328 pickets at 5.5 inches wide. The calculator adds 5% extra pickets for splits and culls.
Concrete for fence posts
Each post hole is a cylinder with the post taking up part of the middle. The calculator finds the hole's volume, subtracts a standard 4x4 post (actual size 3.5 × 3.5 inches), and converts the rest to 50 lb bags of fast-setting post concrete, which yield about 0.375 cubic feet each.
| Hole size | Concrete per hole | 50 lb bags per post |
|---|---|---|
| 8 in wide × 24 in deep | 0.53 cu ft | about 1.4 |
| 10 in wide × 24 in deep | 0.92 cu ft | about 2.5 |
| 12 in wide × 30 in deep | 1.75 cu ft | about 4.7 |
A good rule of thumb is a hole three times the width of the post. Some installers fill only part of the hole with concrete and top it with soil; if you do that, reduce the depth you enter.
Before you dig
- Call 811 (in the US) a few days before digging so buried utility lines can be marked. It's free.
- Confirm your property line and any HOA or city rules on fence height and setbacks.
- Set corner and end posts first, run a string line between them, then set line posts to the string.
- Gate posts take the most stress. Many builders use a larger post or a deeper hole for them.
Frequently asked questions
How far apart should fence posts be?
Wood fence posts are usually set 6 to 8 feet apart, measured center to center. Eight feet is the most common because rails come in 8-foot lengths. Use closer spacing in windy areas or for taller fences.
How deep should fence posts be set?
A common rule is to bury about a third of the post's total length, with at least 2 feet in the ground. A 6-foot fence typically uses 8-foot posts set 2 feet deep. In cold climates, posts should go below the local frost line.
How many bags of concrete per fence post?
For a 4x4 post in a 10-inch hole that's 2 feet deep, expect about 2 to 3 bags of 50 lb fast-setting concrete. Wider or deeper holes need more; the calculator works it out from your hole size.
How many rails does a fence need?
Fences up to about 5 feet tall usually use 2 rails per section. Six-foot and taller privacy fences use 3 rails to stop pickets from warping in the middle.
How many pickets do I need per foot?
With standard 5.5-inch wide pickets set edge to edge, you need about 2.2 pickets per foot of fence. Adding a gap between pickets reduces that number; enter your gap above.