How to use Fence Calculator
The fence calculator estimates the number of posts, rails, pickets and concrete bags needed for any fence length. Enter the total run, post spacing, picket width and rails per bay to get a complete materials list with waste factor.
- Enter total fence length in feet.
- Set post spacing (6 or 8 ft on-centre is standard).
- Enter picket width and gap between pickets.
- Choose number of rails per section.
- Review posts, rails, pickets and concrete bags.
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Post sizing, depth and concrete
Post diameter and depth depend on fence height. For a 6-ft privacy fence, use 4×4 posts set 2 ft deep (or below frost line, whichever is deeper). Use 8-ft posts to allow a 2-ft bury plus a 6-ft above grade. In frost zones (most northern US), set posts 42"+ deep to prevent heaving. Each post hole requires 1–2 bags of fast-setting concrete (50–60 lbs each) depending on hole diameter.
| Fence height | Post size | Bury depth | Post length needed |
|---|---|---|---|
| 3 ft (garden) | 4×4 | 18" | ~5 ft |
| 4 ft (picket) | 4×4 | 24" | ~6.5 ft |
| 6 ft (privacy) | 4×4 or 6×6 | 24–30" | ~8.5 ft |
| 8 ft (tall privacy) | 6×6 | 30–36" | ~11 ft |
Gate framing and hardware
Gates require extra-strong posts (at least 6×6 for a double gate) and gate-specific hardware: heavy hinges (3 minimum for a 6-ft gate), a gate latch, and a drop rod for double gates. Gates wider than 4 ft need diagonal bracing to prevent racking. Allow a 1/2" gap all around for seasonal wood movement.
Worked examples
100 ft privacy fence, 8 ft posts
Inputs: 100 ÷ 8 + 1 posts; 1,200 in ÷ 5.625 in pickets
Result: ≈ 14 posts · ~214 pickets · 2 rails/bay
Concrete for 14 post holes
Inputs: ~2 × 60 lb bags per 4×4 post
Result: ≈ 28 bags fast-setting concrete
Same run at 6 ft post spacing
Inputs: 100 ÷ 6 + 1
Result: ≈ 18 posts (stiffer, more material)
Glossary
- On-centre (OC)
- Distance from the centre of one post to the centre of the next.
- Frost line
- The depth below which soil does not freeze; posts must be set below this level.
- Picket
- The vertical boards forming the fence face; can be flat, dog-eared or pointed.
- Racking
- Lateral leaning or distortion of a gate or fence panel under side loads.
Related reading
Frequently Asked Questions
Why use Fence Calculator?
- Calculates post, rail and picket counts for any fence run length in one step
- Adjustable post spacing lets you compare 6-foot and 8-foot bay material totals
- Concrete bag count per post hole gives a complete below-grade materials estimate
- Picket gap entry returns precise counts for privacy, semi-privacy and open styles
Common use cases
- Order posts, rails and pickets for a 200-foot cedar privacy fence before lumber prices change
- Calculate concrete bags needed to set posts along a sloped backyard boundary
- Compare total picket counts between 3.5-inch and 5.5-inch board widths for the same run
- Estimate materials for a split-rail fence bordering a rural property
- Build a complete materials list for a pool-code-compliant 4-foot picket fence
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