How to calculate fence materials
Everything starts with the length of the fence and the spacing of the posts:
Sections = fence length ÷ post spacing (rounded up)
Posts = sections + 1 + corners + gates
Example: 100 ft of 6 ft privacy fence with posts 8 ft apart and one gate. 100 ÷ 8 = 12.5, so 13 sections and 15 posts. Each section has three rails, so 39 rails, and 1 × 6 pickets laid tight need 219 pickets.
Post holes and concrete
Quikrete’s guidance for setting posts:
- Width: dig the hole about three times as wide as the post. For a 4 × 4 (actually 3 1/2 in square) that’s about 10 1/2 in.
- Depth: bury a third of the post’s total length, which is half the height above ground. A 6 ft fence needs posts 9 ft long set 3 ft deep, so buy 10 ft posts. Where frost goes deeper, follow your local code.
- Drainage: put about 6 in of gravel in the bottom of each hole before setting the post.
The calculator works out the concrete as the volume of the hole minus the post, at 0.375 cubic feet per 50 lb bag of fast-setting mix, and rounds up per hole. That’s a little more than Quikrete’s own rule of thumb, which sets a 3 in post in a 9 × 30 in hole with two bags. For vinyl, Catalyst’s kit uses a 10 in hole for a 5 × 5 post.
| Post and hole | Depth in ground | Concrete | 50 lb bags |
|---|---|---|---|
| 4 × 4 post, 10 1/2 in hole | 2 ft | 1.03 cu ft | 3 |
| 4 × 4 post, 10 1/2 in hole | 3 ft | 1.55 cu ft | 5 |
| 6 × 6 post, 16 1/2 in hole | 3 ft | 3.83 cu ft | 11 |
Lumber sizes
Fence lumber is sold by nominal size, which is larger than the real board. A 1 × 6 picket is 3/4 × 5 1/2 in, a 1 × 4 is 3/4 × 3 1/2 in, a 4 × 4 post is 3 1/2 in square and a 6 × 6 is 5 1/2 in square. The calculator uses the actual widths. Catalyst’s vinyl privacy panels come 6 or 8 ft wide; check the width of the ones you buy.
Before you dig
Call 811 a few days before you dig so buried utility lines are marked, check your property line, and ask whether your town or HOA needs a permit or limits fence height.
For wood priced by the board foot, the board foot calculator adds up posts, rails and pickets. The concrete calculator handles bigger footings, and the deck calculator counts boards and joists for a deck along the same yard.
To have the fence built, the fence installation cost calculator estimates the installed price for wood, vinyl or chain link.