Calculator
Example Data Table
| Scenario | Total run | Offsets | Height | Size | Exposure | Suggested spacing | Total supports |
|---|---|---|---|---|---|---|---|
| Light trellis | 12 m | 0.5 m + 0.5 m | 1.8 m | 90 mm | Moderate | ~2.0 m | 7 |
| Windy fence line | 18 m | 0.5 m + 0.5 m | 2.0 m | 100 mm | High | ~1.8 m | 11 |
| Netting grid | 6 m × 3 m | — | — | — | Moderate | ~1.5 m target | 15 (5×3) |
Examples show typical planning values. Your results depend on inputs and selections.
Formula Used
The calculator first determines the effective run length by subtracting offsets:
Leffective = Ltotal − offsetstart − offsetend
It then uses either your manual max span or an auto-estimated max span:
Smax = Sbase × Fsize × Fheight × Fload × Fmaterial × Fsoil × Fexposure × Fdeflection × Fsafety
The number of segments is chosen so that spacing does not exceed the max span:
n = ceil(Leffective / Smax)
Final spacing and supports are:
spacing = Leffective / n,
supports = n + 1
How to Use This Calculator
- Choose units and your layout mode (line or grid).
- Enter run length and offsets (line mode) or area dimensions (grid mode).
- Add height, size, material, soil, and wind exposure for realistic spacing.
- Use auto max span for estimates, or switch to manual if you already know a limit.
- Click Calculate to see spacing, support count, and position marks.
- Use the download buttons to save your results as CSV or PDF.
Professional Guide
1) Why spacing matters for garden structures
Support spacing controls sag, sway, and long-term durability for trellises, fence lines, arbors, and netting frames. A tighter spacing reduces bending and keeps wires or rails aligned. As a planning reference, light vine trellises often perform well around 1.8–2.4 m spacing, while windy sites or heavy fruiting vines commonly need 1.2–1.8 m.
2) Inputs that change the recommended span
Height increases leverage, so taller posts usually require closer spacing. Post size and material affect stiffness: thicker timber or steel resists deflection better than slim members. The calculator also considers soil condition and exposure because soft ground and high wind increase movement at the base and along the line.
3) Load, deflection, and safety margins
Line load represents combined plant weight, attachments, and seasonal moisture. When you select a stricter deflection limit such as 1/240 instead of 1/120, the tool reduces span to keep the line visually straight and to protect fasteners. Increasing the safety factor likewise lowers spacing for a more conservative layout.
4) Embedment depth and stability
Embedment depth is estimated as a fraction of above-ground height, then adjusted for soil and exposure. For many garden posts, an embedment near 0.35–1.20 m is practical, with deeper settings for soft soil and high wind. Always confirm drainage, frost, and footing choices for your site before installation.
5) Using outputs for marking and procurement
After calculating, the results list support count, spacing, and position marks from your start reference. Use the position table to stake locations, then verify square and alignment with string lines. Export CSV for takeoffs and comparison runs, and export PDF for on-site crews. Re-run scenarios to see how a larger post or lower height changes the plan. Keep notes on weather, plant growth, and repairs to refine future spacing decisions.
FAQs
1) What layout mode should I choose?
Use line mode for fences, trellises, or a single run. Use grid mode for bed frames, netting spans, or rectangular areas where supports repeat in rows and columns.
2) Why does wind exposure reduce spacing?
Higher wind increases lateral force and vibration. Shorter spans reduce bending and limit fastener fatigue, helping the structure stay plumb and the line stay taut.
3) How do offsets affect support count?
Offsets reserve clear space at each end. The calculator subtracts them from total length to get effective run length, then divides that length into equal segments for consistent spacing.
4) Can I override the calculated max span?
Yes. Switch the max span setting to manual and enter your preferred limit. The tool will size the segment count so the final spacing does not exceed your value.
5) What does allowable deflection mean?
It is a straightness limit. A value like 1/240 allows less sag than 1/120. Stricter limits typically reduce spacing to keep rails, wires, or netting lines visually aligned.
6) Is the embedment depth a final construction requirement?
No. It is a planning estimate. Soil type, moisture, frost depth, footing diameter, and post anchoring methods can change the needed embedment. Validate with local practice and site conditions.
7) How should I use the position table?
Measure from your start reference and mark each listed position. Stake the points, check alignment with a string line, then verify post spacing before digging or driving supports.