Seed Spacing Calculator
Calculate how many plants fit in your bed and optimal spacing.
BSc Environmental Science, Certified Master Gardener
Environmental scientist and master gardener with expertise in sustainable home improvements, carbon calculations and horticulture.
Related calculators
About the Seed Spacing Calculator
Proper plant spacing is one of the most overlooked factors in garden productivity. Space plants too close and they compete for light, water, and nutrients — producing smaller yields, more disease (from poor air circulation), and weaker root systems. Space them too far apart and you waste bed space, invite weed colonisation of the gaps, and reduce your total harvest. The ideal spacing balances these competing pressures: close enough to suppress weeds through canopy cover, but far enough to allow each plant to reach its genetic potential.
The triangular offset (staggered row) layout is consistently more space-efficient than a simple grid. By offsetting alternate rows by half a plant spacing, each plant sits in the gap between two plants in the adjacent rows — this is how hexagonal packing works, and it increases the number of plants per square metre by approximately 15.5% compared to grid planting. Raised bed gardeners and market gardeners universally use offset planting for crops like lettuce, spinach, radishes, and carrots where maximising plant count per area is the goal.
Seed packet spacings are conservative — they assume open-ground conditions with variable soil quality. In enriched raised bed compost with consistent watering, most crops can be planted at the closer end of their spacing range. Square foot gardening (popularised by Mel Bartholomew) formalises this into a grid system where each 30cm × 30cm square holds a defined number of plants based on mature size: 1 large plant (broccoli, cabbage), 4 medium plants (lettuce, chard), 9 small plants (spinach, beets), or 16 tiny plants (carrots, radishes). This system works well for beginners because it removes the need to calculate spacing and helps visualise bed capacity.
How it works
Grid: Plants = floor(length / spacing) × floor(width / spacing) Offset row spacing = spacing × 0.866 (= spacing × sin 60°) Even rows: floor(length / spacing) plants Odd rows: floor((length − spacing/2) / spacing) + 1 plants
Where
spacingCentre-to-centre distance between plants in cm0.866sin(60°) — the row compression factor in triangular/offset packingfloor()Round down to the nearest whole numberWorked example
Raised bed: 120 cm long × 90 cm wide. Planting lettuce at 25 cm spacing.
Grid layout: floor(120/25) × floor(90/25) = 4 × 3 = 12 plants.
Offset layout: Row height = 25 × 0.866 = 21.65 cm → floor(90/21.65) = 4 rows.
Even rows (rows 0, 2): floor(120/25) = 4 plants each → 2 × 4 = 8.
Odd rows (rows 1, 3): floor((120 − 12.5)/25) + 1 = 5 plants each → 2 × 5 = 10.
Total offset = 18 plants vs 12 in grid — 50% more in this example.
At 25 cm spacing, this 1.08 m² bed holds 18 lettuces — enough for continuous cut-and-come-again harvesting for a family of four.
Tips to improve your result
- 1.
Always measure spacing from the bed edge. Plants at the border need half their spacing distance from the edge — a 30 cm-spaced plant should sit 15 cm in. Forgetting this either crowds edge plants or wastes a strip of space around the perimeter.
- 2.
Vertical growing doubles effective density for climbing crops. A trellis net allows beans, peas, or cucumbers at 15 cm spacing on a 120 cm bed — far more than the 2–3 plants a standard row spacing allows at ground level.
- 3.
Succession planting uses time as well as space. Plant a second block of lettuce 2–3 weeks after the first — both use the same spacing density but you harvest continuously rather than getting a glut all at once.
- 4.
For root vegetables (carrots, parsnips, beets), seed packet spacings refer to the final spacing after thinning. Sow more densely and thin when seedlings reach 5 cm tall. Thinnings of carrots and beets are edible — do not waste them. Never transplant root crops; thin in place.
- 5.
Companion planting can layer multiple crops in the same space. The traditional "Three Sisters" (maize, beans, squash) effectively achieves three crop layers in one area — the beans also fix nitrogen for the other two, and squash leaves suppress weeds.