How to use the fence calculator
- Measure the fence line from end to end, including where the gates will go. For an L- or U-shaped fence, add the sides together and count the corners.
- Pick post spacing. 8 ft is standard for wood rails and panels. Use 6 ft for extra strength.
- Add gates and their widths. The gate openings are taken off the length that needs pickets or panels.
- Choose pickets or panels. For pickets, set the width and gap. For a privacy fence, set the gap to 0.
- Check the post holes under Adjust assumptions. The concrete count uses those sizes.
The fence formulas
Fence length to fill = total length − (gates × gate width)
Sections = length to fill ÷ post spacing, rounded up
Posts = sections + 1 + corners + gates
Rails = sections × rails per section
Pickets = length to fill × 12 ÷ (picket width + gap), rounded up
Concrete per hole = π × (hole diameter ÷ 2)² × depth − post volume
Worked example
A straight 100 ft picket fence, posts every 8 ft
- Sections = 100 ÷ 8 = 12.5, rounded up to 13.
- Posts = 13 + 1 = 14.
- Rails at 2 per section = 26.
- Pickets 5.5 in wide with 0.5 in gaps: 100 × 12 ÷ 6 = 200 pickets.
- Concrete: a 10 in hole 36 in deep holds 1.64 cu ft; less a 4×4 post leaves 1.38 cu ft. 14 holes × 1.38 = 19.3 cu ft ÷ 0.6 = 33 bags of 80 lb concrete.
Picket count for 100 ft of fence
| Picket | No gap (privacy) | 1/2 in gap | 1 in gap | 2 in gap |
|---|---|---|---|---|
| 3 1/2 in (1×4) | 343 | 300 | 267 | 219 |
| 5 1/2 in (1×6) | 219 | 200 | 185 | 160 |
| 7 1/4 in (1×8) | 166 | 155 | 146 | 130 |
For any other length, divide by 100 and multiply by your length. Always round up.
Choosing post spacing and rails
- 8 ft spacing uses standard 8 ft rails and panels with no waste and the fewest posts.
- 6 ft spacing is stiffer and better for tall privacy fences, windy sites and soft ground.
- Two rails suit fences up to about 4 ft. Three rails keep taller pickets from warping.
- Gate posts carry the most load. Many builders use a larger post or a deeper hole at each side of a gate.
Common mistakes to avoid
- Forgetting the extra post. 13 sections need 14 posts, not 13.
- Ignoring the gate openings. Pickets are not needed across a gate; the gate itself is bought separately.
- Using nominal board width. A “1×6” picket is really 5 1/2 in wide. Using 6 in gives too few pickets.
- Setting posts before checking the line. Confirm the property line and call 811 first.
- Too little concrete. A post hole holds more than it looks. Count your bags before the truck leaves the store.
Frequently asked questions
How many fence posts do I need?
Divide the fence length by the post spacing and round up to get the number of sections, then add one. Add one more for each corner and each gate opening. A straight 100 ft fence with posts every 8 ft has 13 sections and 14 posts.
How many pickets do I need for 100 feet of fence?
Convert the fence length to inches (multiply by 12) and divide by the picket width plus the gap. With 5.5 in pickets and a 0.5 in gap: 1,200 ÷ 6 = 200 pickets. For a privacy fence with no gap, 1,200 ÷ 5.5 = 219 pickets.
How far apart should fence posts be?
Most wood fences use 6 to 8 ft between post centers. 8 ft matches standard rail and panel lengths. Closer spacing makes a stronger fence in windy or soft-soil areas. Vinyl and metal systems often specify their own spacing.
How much concrete do I need per fence post?
For a 4×4 post in a 10 in hole 3 ft deep, about 1.4 cubic feet, which is a little over two 80 lb bags. Bigger holes and 6×6 posts need more. Change the hole size under Adjust assumptions.
How deep should fence posts be?
A common rule of thumb is about one third of the post length in the ground, and below the frost line in cold climates. Local rules and fence height decide the real answer, so check before you dig.
Do I need a permit for a fence?
Often, yes, especially over a certain height or in front yards, and many HOAs have their own rules. Check with your city or county and confirm your property line before you set the first post.