How to use the fence calculator
- Measure the full run of the fence in feet, including where gates will go.
- Choose your post spacing. 8 ft is standard for wood fences; use 6 ft for heavier fences, windy sites or to match 6 ft panels.
- For a picket or board fence, enter the picket width and the gap you want. For a privacy fence the gap is 0.
- Enter the post hole size to get concrete. Check your local frost depth: posts should go below it.
Fence formulas
sections = ⌈length ÷ post spacing⌉
posts = sections + 1 + gates
pickets = length × 12 ÷ (picket width + gap)
rails = sections × rails per section
Each gate gets one extra post so both sides of the opening are supported. Corners in a straight-line estimate are covered because every section ends on a post; add one post per extra corner if your fence turns between post positions.
Concrete per fence post
| Post | Hole | Concrete | 80 lb bags |
|---|---|---|---|
| 4×4 | 10 in × 2 ft | 0.9 cu ft | 2 |
| 4×4 | 10 in × 3 ft | 1.4 cu ft | 3 |
| 6×6 | 12 in × 3 ft | 1.7 cu ft | 3 |
| 6×6 | 12 in × 4 ft | 2.3 cu ft | 4 |
Many fence builders put 3–4 inches of gravel in the bottom of each hole for drainage. You can estimate it with the gravel calculator.
Before you dig
- Call 811 (in the US) a few days ahead to have buried utility lines marked. It's free.
- Confirm your property line and any setback, height or HOA rules.
- Use ground-contact rated pressure-treated posts.
Frequently asked questions
How many posts do I need for a 100 ft fence?
With 8 ft spacing, 100 ft is 13 sections, so you need 14 posts, plus one more for each gate.
How many pickets do I need for a 100 ft privacy fence?
With 5.5 inch pickets and no gap, 100 ft × 12 ÷ 5.5 = 219 pickets. Buy about 5% extra for splits and culls.
How deep should fence posts be?
A common rule is one third of the post’s height above ground, and at least below your local frost line. A 6 ft fence typically uses 8 ft posts set 2 to 3 ft deep.