Inputs
Example data table
| Structure | Layout | Size (L×W) | Offset | Spacing (L/W) | Safety | Estimated piles |
|---|---|---|---|---|---|---|
| Raised bed | Perimeter only | 3.60 m × 1.20 m | 0.15 m | 0.90 m / 0.90 m | 10% | 12 |
| Garden deck | Full grid | 4.80 m × 3.00 m | 0.20 m | 1.20 m / 1.00 m | 15% | 24 |
| Pergola | Perimeter only | 3.00 m × 3.00 m | 0.20 m | 1.50 m / 1.50 m | 10% | 8 |
Formula used
How to use this calculator
- Pick a structure type to label your report.
- Select a layout: full grid for platforms, perimeter for light builds.
- Choose units, then enter your length and width.
- Set an edge offset to keep piles away from edges.
- Enter your desired spacing along length and width directions.
- Apply a safety factor for soil uncertainty and spare parts.
- Optionally add total load to see load per pile.
- Press Calculate; download CSV or PDF for records.
Project layout assumptions
The calculator models a rectangular garden footprint and places piles on a regular grid inside an edge offset. It converts your target spacing into an integer count of rows and columns, ensuring at least two in each direction for stability. Full grid mode counts every intersection, while perimeter mode counts edge points and subtracts duplicated corners.
Spacing strategy for garden loads
Closer spacing increases pile count and reduces bending demand in joists or bearers, which helps decks, shed bases, and heavy planters. Wider spacing reduces cost but can increase deflection and vibration. Many light garden platforms use about 1.0–1.5 m spacing, while heavier surfaces may tighten to 0.8–1.2 m. Use manufacturer guidance for framing spans, then align spacing with practical beam layouts.
Edge offset and perimeter stability
Offsets keep piles away from the perimeter where soil is more disturbed by excavation, edging, and irrigation. A modest offset also provides room for perimeter boards and drainage. Typical offsets range from 0.10–0.30 m, depending on edging thickness and beam width. If the offset becomes too large for the footprint, the usable area shrinks and spacing must tighten to keep corner support.
Safety factor and procurement planning
The safety factor increases the base count to cover placement tolerance, small layout changes, and field waste. For soft soils, sloped yards, or unknown fill, a higher percentage provides contingency without redesign. Common allowances are 5–20% for small projects, and higher when access is difficult. When “even rounding” is enabled, the final count is adjusted to support symmetric ordering and consistent bracing patterns.
Interpreting the load-per-pile check
If you enter a total design load, the tool reports average load per pile after the safety factor is applied. This is a screening value only; real piles see uneven loading from concentrated planters, furniture, and edge beams. Compare the average to your chosen pile’s rated capacity, including any reduction for weak soils.
FAQs
1) When should I choose full grid instead of perimeter mode?
Use full grid for decks, sheds, and heavy planters where loads spread across the surface. Choose perimeter mode for light frames where edge beams carry most weight and the interior span is short.
2) What spacing should I start with for small garden platforms?
Start around 1.0–1.5 m for light platforms, then tighten if beams span farther than recommended. If you notice bounce or large spans, reduce spacing along the main framing direction first.
3) Why does edge offset affect the pile count so much?
Offsets reduce the usable grid area inside the footprint. Less usable distance means more rows or columns are needed to maintain the same spacing, increasing the count, especially on compact layouts.
4) What safety factor is reasonable for typical garden work?
Many projects use 5–15% to cover tolerance and minor changes. Increase it when soils are soft, access is tight, or you expect last‑minute layout adjustments during installation.
5) How should I use the load-per-pile value?
Treat it as an average check only. Compare it to the pile’s rated capacity and keep margin for weak soil and concentrated loads. For critical builds, confirm design loads with local practice.
6) Can I mix units for length and load?
Yes. Select meters or feet for dimensions, then choose kN or pounds for load. The calculator converts values internally so the reported load-per-pile is consistent in kN.