Common Mistakes When Building a Fence (Posts, Gates, Concrete)
A fence is simple on paper and unforgiving in the ground. A 100 ft fence, 6 ft tall, with posts 8 ft apart and one 4 ft gate takes 14 posts of 8 ft, 12 sections, 36 rails and 24 bags of concrete. Use the fence calculator for your layout.
Part of the project planner: Planning and building a fence.
Mistake 1: choosing the post spacing by eye
Rails and panels set the spacing, and wider spacing sags over time. Eight feet is common for wood panels and six feet is stronger. The 100 ft example:
| Post spacing | Posts | Sections | Rails | Bags of concrete |
|---|---|---|---|---|
| 6 ft | 18 | 16 | 48 | 31 |
| 8 ft | 14 | 12 | 36 | 24 |
Mistake 2: forgetting the gate posts
A gate needs a stronger post at each side, and the gap breaks up the run. Each gate changes the count:
| Gates | Posts | Sections | Pickets |
|---|---|---|---|
| 0 | 14 | 13 | 219 |
| 1 | 14 | 12 | 210 |
| 2 | 15 | 12 | 201 |
Mistake 3: posts that are too short
Part of every post goes into the ground, so the post is longer than the fence is tall. The example by fence height:
| Fence height | Post length | Bags of concrete |
|---|---|---|
| 4 ft | 6.0 ft | 24 |
| 5 ft | 7.0 ft | 24 |
| 6 ft | 8.0 ft | 24 |
| 8 ft | 10.7 ft | 32 |
Mistake 4: setting posts out of line or out of plumb
- Run a string line between the end posts, and set the others to it.
- Check each post for plumb on two sides before the concrete sets, and brace it.
- Slope the top of the concrete away from the post so that water runs off.
- Let the concrete cure as the bag says before you hang panels, or the posts will lean.
Mistake 5: skipping the line, the rules and the call
Fence on your own side of the boundary, check any setback or height limit, and call the local utility locator service before you dig, which is free in most places. See the fence materials calculator for the full list and the fence post concrete calculator for the concrete. Estimates only.
Frequently asked questions
How many posts do I need for 100 ft of fence?
With posts 8 ft apart and one 4 ft gate, 14 posts, in 12 sections.
How deep should fence posts be?
Often about a third of the post length, and below the frost line in cold areas. A 6 ft fence uses 8 ft posts for that reason. Check your local rules.
How much concrete does a fence post need?
The calculator counts 24 bags of 50 lb mix for the whole 100 ft example. See the fence post concrete calculator for one post.
Do I need a permit for a fence?
Often there is a height limit or a setback rule, and some areas require a permit. Check with your local authority, and the property line, before you dig.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.