A picket fence is four separate counts that share one input, the length of the run. Posts and rails depend on how far apart the posts go. Pickets depend only on the length, the picket width and the gap.
Sections = fence length ÷ post spacing, rounded up
Posts = sections + 1
Rails = sections × rails per section
Pickets = fence length ÷ (picket width + gap), × (1 + extra)
An 80 ft run with 8 ft spacing
Eighty divided by eight is ten sections, which need eleven posts. With three rails per section that is thirty rails. For the pickets, a 5½ in picket with a ½ in gap uses 6 inches per picket, so 80 ft (960 in) holds 160 pickets before extra. The planner shows the figures this way:
Worked example 80 ft straight run, 8 ft spacing, 3 rails, 5½ in pickets with ½ in gaps
| Material | Calculated | Buy |
|---|---|---|
| Postsone straight run, no corners or gates | 10 sections + 1 | 11 posts |
| Rails3 per section × 10 sections | 10 × 3 | 30 rails |
| Pickets5.5 in pickets with 0.5 in gaps, 5% extra | 160 pickets before extra | 168 pickets |
This example assumes
- One straight run with no corners or gates
- 8 ft post spacing, chosen as an example
- 5% extra on pickets, an editable planning default
With the 5% extra the list rounds the total up to 168 pickets.
Nominal width is not actual width
Lumber names are larger than the boards. A nominal 1×6 picket is about 5½ inches wide, and a nominal 1×4 about 3½, as lumber standards describe. If you plan by the nominal number, your picket count will come out short. Measure the picket you are buying.
What a straight-run estimate misses
Corners need extra posts and sometimes different spacing. Gates need hardware and their own posts. The ends of a run can be different from the middle. The planner counts one continuous straight run and leaves the rest to you, so treat each straight section separately and add corners and gates yourself.
What changes the estimate?
- Post spacing from your fence system’s instructions, not from a default
- Picket width and gap, measured on the actual pickets
- Corners, gates and end posts, which sit outside a straight-run count
- The extra you add for cuts and damaged boards
- Concrete or other post footings, which the planner counts only if you enter a number
This guide counts materials. It does not say how far apart posts must be for your fence to be sound. Use your fence system’s instructions and your local requirements.