Calculator
Example data table
| Raft (L×W) | Margin | Layout | Target spacing | Estimated result |
|---|---|---|---|---|
| 120×60 cm | 5 cm | Rectangular | 20×20 cm | 6×3 = 18 holes |
| 200×100 cm | 7 cm | Hex | 25 cm (X) | ~8×4 ≈ 32 holes |
| 90×50 cm | 4 cm | Rectangular | 15×18 cm | 6×3 = 18 holes |
Formula used
Available area
- Available length = L − 2M
- Available width = W − 2M
Rectangular grid (spacing-first)
- Columns = floor(Available width ÷ Sx) + 1
- Rows = floor(Available length ÷ Sy) + 1
Hex (staggered) packing
- Row spacing ≈ 0.866 × Sx (equilateral packing)
- Odd rows shift right by Sx ÷ 2
How to use this calculator
- Select units that match your tape measure.
- Enter raft length, width, and edge margin.
- Set hole diameter and desired clearance.
- Pick a layout: rectangular or staggered hex.
- Choose a mode: target spacing or plant count.
- Press Calculate to see rows, columns, and coordinates.
- Download CSV for drilling templates or CNC guides.
- Download PDF to share the plan with helpers.
Professional notes
Why hole spacing drives crop performance
Consistent center spacing improves light capture, airflow, and nutrient access in raft systems. When plants crowd, leaves overlap and humidity rises, increasing disease pressure. When spacing is too wide, raft area is underused and water temperature can fluctuate faster.
Selecting margins for strength and handling
Edge margin keeps holes away from weak raft edges and leaves room for handling, labels, and float seams. A practical margin is 5–8 cm for common foam boards, but larger rafts or heavy net pots benefit from more. Measure from the edge to the hole center for repeatable drilling.
Rectangular grids versus staggered packing
Rectangular grids are easy to mark with a tape and square, and they match most drilling jigs. Staggered layouts place every other row halfway between holes, improving packing while maintaining access. In staggered patterns, row spacing is about 0.866 times the horizontal spacing, so density increases without reducing center distance along the row.
Setting realistic spacing targets
Leafy greens often work well around 15–20 cm centers, while larger herbs and fruiting plants usually need 20–30 cm or more. Use the calculator’s minimum check based on hole diameter plus clearance to avoid overlapping pots and cracked foam. If you plan to add collars or insulation, include that in clearance.
Turning results into reliable templates
After calculating rows and columns, use the coordinate preview to verify that the first and last holes sit inside your margins. Export the CSV to create a drilling guide, CNC pattern, or printed layout. The PDF summary is useful for field teams, ensuring the raft is drilled consistently across batches. For quick planning, start with target spacing, then compare the hole count with your seedling schedule. If you must hit a specific count, switch to plant-count mode and review the achieved spacing. Always test drill one raft, drop in net pots, and confirm roots have room before producing many boards. Save settings so future rafts match.
FAQs
1) What is center-to-center spacing?
It is the distance from one hole center to the next. It controls plant density and keeps net pots from touching.
2) How should I choose an edge margin?
Measure from the raft edge to the first hole center. Leave enough foam for strength, handling, and labeling. Five to eight centimeters works for many rafts.
3) When is a staggered layout useful?
Choose staggered rows when you want higher density without shrinking the along-row spacing. It also improves access between plants compared with a tight square grid.
4) Why do I see a minimum spacing warning?
The calculator checks hole diameter plus clearance. If centers are smaller than that value, holes can overlap, foam can crack, and pots may bind during installation.
5) Can I work in inches and still get a drill file?
Yes. Outputs display in your selected units, while the CSV stores coordinates in millimeters for consistent templates across software and printers.
6) Why are only some coordinates previewed?
Large rafts can create hundreds of holes. The preview limit keeps the page fast, while the CSV download always includes the full coordinate list.