Fence Post Spacing Calculator — How Many Posts & How Much Concrete?
Enter your fence length to get post count, hole depth, and concrete bags for the whole run. No sign-up, no data stored.
Post & concrete plan
How fence post quantities are calculated
- Posts = fence length ÷ spacing, rounded up, plus 1 for the end post. 100 ft ÷ 8 = 12.5 → 13 posts.
- Hole depth = post height above ground ÷ 3. A 6-ft post gets a 24-in hole (measure below frost line if that's deeper).
- Concrete = posts × bags per hole. At 2.5 bags per hole, 13 posts need about 33 bags of 50-lb mix.
- Add extra: corners, gates and ends each take a post — count them in the run, and add 1–2 spare posts for errors.
Set every hole below the frost line in cold climates and put 2–4 inches of gravel in the bottom for drainage. Brace corner and gate posts — they carry the most tension.
Fence length → post count reference
Posts at 8-ft spacing, plus hole depth and concrete for 6-ft posts.
| Fence length | Posts | Hole depth | 50-lb bags (2.5/hole) |
|---|---|---|---|
| 50 ft | 8 | 24 in | 20 |
| 100 ft | 13 | 24 in | 33 |
| 150 ft | 19 | 24 in | 48 |
| 200 ft | 25 | 24 in | 63 |
| 300 ft | 37 | 24 in | 93 |
Last updated: October 2026 · Estimates assume 8-ft spacing and 6-ft posts. Frost line, soil and gate weight change the numbers — verify locally before buying.
Fence post FAQ
Only for light ranch rail or temporary fences. 10-ft spans sag with wood pickets or any wind load. Stick to 8 ft on center for a wood privacy fence.
It varies from 12 inches in the South to 48+ inches in the far North. If your hole depth from the 1/3 rule is shallower than the local frost depth, dig to the frost depth instead.
Concrete is the reliable choice for corner, gate and end posts. Interior posts can be set in packed gravel in good soil, but concrete everywhere is easier and more durable.
One heavy post on each side of the opening, set deeper and with more concrete (often 3+ bags) because the gate swings its whole weight on them.
4×4 pressure-treated is standard for 6-ft fences. Use 6×6 for tall or windy fences, or for heavy gates. Bigger posts need wider holes — an 8-in hole is the minimum for 4×4.
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