Calculator Inputs
Example Data Table
| Row Length | Spacing | Rows | Height | End Bracing | Mid Bracing | Wire Levels |
|---|---|---|---|---|---|---|
| 12 m | 2.4 m | 1 | 1.8 m | Yes | No | 3 |
| 25 m | 2.0 m | 2 | 2.0 m | Yes | Yes (10 m) | 4 |
| 40 m | 3.0 m | 1 | 2.2 m | No | Yes (12 m) | 3 |
Formula Used
Leff = L − (Nopen × Wopen)
Posts = ceil(Leff / S) + 1 (keeps actual spacing ≤ target spacing S)
D = max(H × r, Frost) where H is above‑ground height and r depends on soil (or your custom ratio).
PostLength = H + D + Allowance
V = π × (d/2)² × D. Total volume: Vtotal = V × TotalPosts.
Wire = Leff × Rows × Levels × (1 + Extra%)
How to Use This Calculator
- Choose your unit system, then enter the trellis row length and number of rows.
- Set a target post spacing based on crop load and material stiffness.
- Add openings if you need gates or access points along the row.
- Enter the above‑ground trellis height, then choose soil type (or a custom embed ratio).
- Enable end bracing for stronger anchors; add mid braces for long runs.
- If you plan to set posts in concrete, enable it and enter hole diameter and bag yield.
- Press Calculate to see results above the form, then export CSV or PDF.
Post spacing and load planning
Trellis spacing controls both stability and material cost. A tighter spacing reduces bending in each post when vines are heavy,
especially after irrigation or rain. This calculator keeps the real spacing at or below your target by using
ceil(Leff/S)+1, so you get predictable intervals even when the row length is not a perfect multiple.
For light climbers, wider spacing can be acceptable, but tall trellises and fruiting crops usually benefit from shorter spans.
Embed depth and frost consideration
A common rule is to bury a fraction of the above-ground height, then compare it to local frost depth. The embed depth here is
calculated as max(H×r, Frost). The soil ratio increases in soft ground where rotation is more likely and decreases in
dense, rocky soils where holes are difficult to deepen. If you already follow a site standard, enter a custom ratio to match it.
Bracing strategy for long runs
End bracing improves anchor resistance where wire tension concentrates. Mid bracing is recommended for long rows or high wire counts because cumulative tension can creep over time. The calculator estimates brace sets by interval and adds posts per set, helping you decide whether incremental bracing is cheaper than over-sizing every line post.
Concrete and hole sizing for consistent alignment
When concrete is selected, the model treats each hole as a cylinder: V=π(d/2)²×D. This provides a practical estimate
for mix volume and bag count, useful for procurement and staging. Concrete is not mandatory in all gardens, but it can improve
plumb alignment, reduce seasonal movement, and increase service life in wet locations.
Example dataset and interpretation
Example data: Row length 25 m, spacing 2.0 m, rows 2, height 2.0 m, openings 1×1.0 m, end bracing yes, mid bracing yes at 10 m, wire levels 4, wire extra 10%, concrete yes with 25 cm holes. The effective length becomes 24 m, which drives line-post count and wire length. Review the “Suggested Post Length” output to confirm your stock size before purchase.
FAQs
1) Why does the calculator add one extra post per row?
Posts are counted at both ends of the effective row. Using ceil(Leff/S)+1 ensures the last segment is not longer than your target spacing.
2) Should I always enable end bracing?
End bracing is strongly recommended for tensioned wire systems and heavier vines. For light trellises with rigid panels, it can be optional if posts are stout and embedment is adequate.
3) What embed ratio should I use for soft soil?
Soft or sandy soils typically benefit from deeper embedment. Start around 0.40 of above-ground height, then compare against frost depth and adjust using your field experience.
4) How does frost depth change the result?
If frost depth exceeds the ratio-based embedment, the calculator uses frost depth. This reduces heave-related movement and helps preserve vertical alignment across seasons.
5) Do openings reduce the number of posts?
Yes. Openings subtract width from the effective length, which can reduce line-post count and wire length. Bracing decisions still apply to the remaining run.
6) How accurate is the concrete bag estimate?
It is a planning estimate based on cylindrical hole volume and your bag yield setting. Real usage varies with over-excavation, rock voids, and mix slump, so keep a small contingency.
7) What wire extra percentage is reasonable?
Ten percent is a common starting point for terminations and tensioning. Increase it for complex anchors, multiple turns, or when you prefer generous tails for future re-tensioning.