Hong Life CalculatorsUnderstanding the plant spacing calculator — concept and principle
This calculator works out how many plants fit in a bed at a given spacing, on a square grid or a staggered (triangular) grid, plus plants per square metre and per square foot. Gardeners and landscapers use it to order bedding plants, ground cover, bulbs or vegetable transplants.
How it is calculated
- Area per plant on a square grid = s², where s is the spacing.
- Area per plant on a triangular grid = s² × √3 ÷ 2 ≈ 0.866 s².
- Plants = bed area ÷ area per plant, rounded up.
- Plants per m² = 1 ÷ area per plant; per ft² = 0.0929 ÷ area per plant.
- Feet and inches are converted with 1 ft = 0.3048 m and 1 in = 2.54 cm.
The principle
On a square grid each plant sits at the corner of a square with sides equal to the spacing, so each plant "owns" one square. On a triangular grid, also called staggered or offset planting, plants sit at the corners of equilateral triangles; every plant is the same distance from all six neighbours, and each one owns a hexagon of area 0.866 s². That packs about 15.5% more plants into the same bed and gives an even, natural look with no straight gaps. Extension services use the same area-per-plant method to estimate plant quantities.
Worked example
Default inputs: metric, bed 12 m², spacing 30 cm, square grid.
- Area per plant = 0.30 × 0.30 = 0.09 m².
- Plants = 12 ÷ 0.09 = 133.3, rounded up to 134.
- Plants per m² = 1 ÷ 0.09 = 11.11; per ft² = 0.0929 ÷ 0.09 = 1.03.
- Square grid, so no extra plants versus square (0).
| Spacing between plants (cm or inches) | Plants needed |
|---|---|
| 7.5 | 2,134 |
| 15 | 534 |
| 22.5 | 238 |
| 30 | 134 |
| 37.5 | 86 |
| 45 | 60 |
| 60 | 34 |
How to read the result
Use the spacing on the plant label, which reflects mature size. Closer spacing fills in faster but costs more and may need thinning; wider spacing saves money but leaves bare ground longer. Buy a few extra to replace losses, and allow for edges, where half a spacing from the border is usual.
Common mistakes
- Mixing centimetres and metres, or inches and feet.
- Using a triangular count but planting in square rows.
- Forgetting paths, stepping stones or existing plants in the bed area.
- Using spacing for young plants instead of mature spread.
Frequently asked questions
How many plants fit in 1 m² at 30 cm spacing?
About 11 on a square grid, or about 13 on a triangular grid.
Is triangular spacing better?
It fits about 15.5% more plants at the same spacing and covers the ground more evenly.
What spacing should I use?
Follow the plant label, which is based on mature size.
Sources: Iowa State University Extension, "How to Determine Plant Quantity for Planting Beds" · NIST Special Publication 811 (2008), Appendix B (1 ft = 0.3048 m)