Quick answer: measure the fence line, subtract gate openings, and divide by your post spacing to get the number of sections. You need one post more than sections, plus one for each corner and gate. Then add panels or rails and pickets, and concrete for each post hole. The fence calculator does all of this at once.
1. Measure the fence line
- Mark the line with stakes and a string line, and measure along it.
- Note every corner (change of direction) and every gate, with its width.
- Before you finalise the line, check your property boundary and any local height or HOA rules.
2. Choose the post spacing
| Fence | Typical post spacing |
|---|---|
| Ready-made panels (US) | 8 ft, the panel width |
| Ready-made panels (UK) | 6 ft / 1.83 m |
| Board-on-rail (picket, privacy) | 6–8 ft |
| Windy or exposed sites | Toward the shorter end |
3. Count sections and posts
- Fencing length = total length − gate widths.
- Sections = fencing length ÷ post spacing, rounded up.
- Posts = sections + 1, plus 1 per corner and 1 per gate.
Gate posts take the most strain. Many builders use a larger post (for example a 6×6 instead of a 4×4) and a deeper hole for gates.
4. Panels, or rails and pickets
- Panel fence: panels = sections.
- Board fence: rails = sections × rails per section (2 for low fences, 3 for 5–6 ft fences). Pickets = fencing length ÷ (picket width + gap).
For a privacy fence with no gaps, set the gap to zero, then add 5–10% extra pickets for warped or split boards.
5. Post holes and concrete
| Post | Hole diameter | Hole depth |
|---|---|---|
| 4×4 (3.5”) | 10–12” | About ⅓ of the above-ground height, 24” minimum |
| 6×6 (5.5”) | 12–16” | Same, and deeper for gate posts |
| 100 mm | 300 mm | About ⅓ of the height, 600 mm minimum |
In cold climates, set posts below the frost line so frost heave can’t push them up. Ask a local building department or supplier for the frost depth in your area.
Concrete per hole is the hole volume minus the post. For a 4×4 in a 10” × 30” hole, that’s about 1.4 cu ft, roughly four 50 lb bags of fast-setting mix.
Worked example: 100 ft with one gate and two corners
| Step | Result |
|---|---|
| Fencing length | 100 − 4 ft gate = 96 ft |
| Sections at 8 ft | 96 ÷ 8 = 12 |
| Posts | 12 + 1 + 2 corners + 1 gate = 16 |
| Panels | 12 |
| Concrete | 16 × ~1.4 cu ft ≈ 22 cu ft, or about 59 bags of 50 lb fast-setting |
Before you dig
- Book a utility locate (call 811 in the US) a few days before digging, so you don’t hit buried cables or pipes.
- Set the corner and end posts first, then run a string line between them to line up the rest.
- Use ground-contact-rated treated lumber, or set metal posts, for anything in the ground.
FAQ
How many fence posts do I need for 100 feet?
With 8 ft spacing and no gates or corners, 14 posts: 13 sections + 1.
Do I put concrete in every post hole?
Most fences do. Some builders use compacted gravel instead, which drains better. Gate and end posts benefit most from concrete.
Should fence posts be 8 or 6 feet apart?
8 ft is standard for most wood fences and matches common US panels. 6 ft makes a stiffer fence and suits tall privacy fences or windy sites.
How this guide was written: spacing and hole sizes are common building rules of thumb. Local building codes, frost depth and the fence manufacturer’s instructions take priority. See how I test and review.