Plant Spacing Calculator

What Is a Plant Spacing Calculator?

A plant spacing calculator converts the recommended distance between plants into the number of plants needed to fill a bed, border, or field. It also works in reverse: given the number of plants you have, it tells you how large an area they will cover at the correct spacing. The calculation is needed because the relationship between spacing and plant count is not intuitive - small changes in spacing have large effects on plant numbers, and the two common spacing dimensions (in-row and between-row) must be multiplied together, not averaged.

Spacing recommendations for vegetables and flowers are specific to each species and cultivar, and following them matters in both directions. Planting too closely produces competition for light, air, and nutrients: the individual plants are smaller, yields are lower, and pest and disease pressure increases as airflow through the canopy is reduced. Planting too widely wastes bed space and, for crops that need block planting for pollination (sweet corn), can reduce fruit set. Getting the spacing right from the start is far more efficient than transplanting or thinning after establishment.

The calculator supports three planting patterns: square or block planting (standard for most vegetables), triangular offset planting (used in ornamental borders and some commercial flower crops), and row planting with different in-row and between-row spacing (standard for most vegetable rows and field crops). It includes presets for 15 common vegetables and flowers, with spacing recommendations consistent with Royal Horticultural Society vegetable growing guidance. For large-scale field crop populations, our plant population calculator works at hectare and acre scale with additional crop presets.

How to Use the Plant Spacing Calculator

1. Choose between presets and custom spacing. Select Plant / Crop Presets to load the recommended spacing for 15 common plants. Select Custom Spacing to enter your own dimensions from a seed packet, nursery label, or variety guide.
2. Select or enter your spacing. For preset plants, the spacing is loaded automatically along with a description of the recommended arrangement. For custom spacing, choose your pattern (square, triangular, or row) and enter the spacing in centimetres, metres, inches, or feet.
3. Enter your bed or border area. Measure the bed in square metres, square feet, or square yards. The calculator shows the number of plants for that area and adds 10% to the order quantity as contingency for losses in transplanting, poor establishment, and replacements.
4. Optionally enter plants available. If you already have a fixed number of plants (transplants bought, seeds germinated), enter the quantity and the calculator shows how many square metres they will fill at the selected spacing. This reverse calculation is useful when planning bed layouts around available stock.
5. Read the layout guide. Below the results, the calculator shows the number of rows across a 1 m wide bed and the number of plants per linear metre of row, which makes it easy to mark out the planting positions with a measuring stick before setting plants in the ground.

Formula and Methodology

For square or row planting:

Plants per m² = 1 ÷ (spacing A in m × spacing B in m)
Total plants = plants per m² × area in m²
Order quantity = ceiling(total plants × 1.10)

For triangular (offset row) planting:

Plants per m² = 2 ÷ (√3 × spacing²) ≈ plants per m² × 1.1547
(15% more plants than a square grid at the same spacing)

Reverse calculation (area from available plants):

Area (m²) = available plants ÷ plants per m²

Worked example: 8 m × 1.2 m raised bed (9.6 m²), mixed lettuce and beetroot.

• Lettuce at 30 cm square: 1 ÷ 0.09 = 11.1 plants/m²; 9.6 × 11.1 = 107 lettuces; order 118
• Beetroot at 10 cm × 20 cm: 1 ÷ 0.02 = 50 plants/m²; 4.8 m² section × 50 = 240 beetroot seeds; order 264

The layout guide for beetroot: a 1.2 m wide bed has 1.2 ÷ 0.20 = 6 rows across, each with 1 plant every 10 cm = 10 plants per metre of row.

Spacing Recommendations for Common Plants

Tomatoes are planted at 60 cm in-row and 90 cm between rows for cordon (indeterminate) varieties trained up vertical supports. Bush (determinate) tomatoes need less vertical space but equal or greater horizontal spacing, 45–60 cm each way. In a polytunnel or greenhouse where height is maximised, cordon varieties are spaced more tightly on the row (45 cm) with the same 90 cm between rows. Always allow for the mature plant size, not the transplant size.

Brassicas (cabbage, broccoli, kale, cauliflower) are spaced at 45–60 cm depending on head size. Large drumhead cabbages and cauliflower need 60 cm in each direction. Calabrese and sprouting broccoli need 45 cm. Chinese cabbage and spring greens can be grown at 30 cm. All brassicas benefit from firm planting in well-consolidated soil and netting against cabbage white butterfly from planting onwards.

Root vegetables are sown directly rather than transplanted. Carrots are sown thinly in rows 20 cm apart and thinned to 5 cm apart in the row. Parsnips follow the same spacing. Beetroot is thinned to 10 cm in rows 20 cm apart. Turnip and swede need 20–25 cm in the row and 30–35 cm between rows. Sowing direct means the plants-per-m² calculation is used to estimate seed quantity rather than transplant quantity: sow at 3–4× the final plant density and thin to the correct spacing.

Ornamental flowers vary significantly by plant type. Lavender, salvias, and other sub-shrubs need 45–90 cm depending on mature spread. Summer bedding (petunias, marigolds) is planted at 20–30 cm for a dense display. Dahlias require 60–90 cm for large-flowered varieties. Bulbs (tulips, daffodils) are planted at 10–15 cm within dense blocks and 15–20 cm between blocks in a naturalistic planting.

Real-World Applications

Kitchen gardener planning a new raised bed: A gardener has built a 4 m × 1.2 m raised bed (4.8 m²) and wants to grow tomatoes, courgettes, and lettuce. Tomatoes: 60 × 90 cm = 1.85 plants/m²; for 1.8 m² of the bed: 3 plants. Courgettes: 90 cm square = 1.23 plants/m²; for 1.5 m²: 2 plants. Lettuce: 30 cm square = 11.1 plants/m²; for 1.5 m²: 17 lettuces. Total transplants to order: tomatoes 3 + 10% = 4; courgettes 2 + 10% = 3; lettuce 17 + 10% = 19. The calculation prevents over-ordering plug plants (which are perishable) and ensures the bed is planted at the correct density.

Flower farmer planting a cutting bed: A cut flower grower is planting 60 m² of dahlias for a roadside stall. Dahlia spacing for dinner-plate varieties: 90 cm square. Plants/m²: 1 ÷ 0.81 = 1.23. Total tubers: 60 × 1.23 = 74; order 82 (10% contingency). At £2.50 per tuber: £205 in planting stock. The reverse calculation also works: she has 50 tubers available and wants to know the area they cover. 50 ÷ 1.23 = 40.7 m². She plans accordingly and orders 25 additional tubers to fill the remaining 20 m² of the plot.

Allotment society planning a committee bed: A committee is planning a 15 m² demonstration bed at an allotment site with 30 onion sets, 50 carrot seeds, and a tray of 36 lettuce plugs already available. Onion: 10 × 30 cm = 33.3/m²; 30 sets cover 0.9 m². Carrot: 5 × 20 cm = 100/m²; 50 seeds cover 0.5 m². Lettuce: 30 × 30 cm = 11.1/m²; 36 plugs cover 3.2 m². Total from available stock: 4.6 m². The remaining 10.4 m² can be planted with additional crops once the committee agrees the bed layout. The calculator makes the area allocation explicit before physical marking begins.

Market garden comparing square vs triangular planting for strawberries: A grower is comparing 40 cm square planting (6.25 plants/m²) vs 40 cm triangular planting (7.22 plants/m²) on a 200 m² strawberry bed. Square planting: 200 × 6.25 = 1,250 plants. Triangular: 200 × 7.22 = 1,444 plants. Difference: 194 plants at £0.45 per runner = £87 additional planting cost. The expected yield increase from 15% more plants per m² must justify the additional cost. At an average yield of 250 g/plant and a farm-gate price of £3/kg, the extra 194 plants produces 48.5 kg = £145.50 additional revenue, making the triangular layout financially worthwhile before accounting for any management cost difference.

Common Mistakes and Troubleshooting

Planting to current size rather than mature size: Courgette transplants look very small at 15 cm tall, but at maturity they spread 90–120 cm. A bed that looks well-planted with 20 cm spacing in May will be a congested mass of competing plants by July. Always use the mature plant spacing from the seed packet or variety guide, not the transplant size.

Failing to mark out rows before planting: Placing transplants by eye, even with the best intentions, invariably produces uneven rows and irregular spacing. The result is poor light distribution across the bed and difficulty with hoeing and maintenance. Mark row positions with garden twine stretched between canes before planting, and use a spacing stick marked at the correct in-row distance to position each plant.

Calculating area without excluding paths and irrigation infrastructure: A 10 m × 2 m growing area sounds like 20 m², but if there is a central path of 0.5 m width, the growing area is actually 10 × 1.75 m × 2 (each side) = 17.5 m² of plantable space. Measure the actual bed area, not the overall plot size, before calculating plant numbers.

Not accounting for germination rate when ordering seed: Unlike transplants (where each plug is a viable plant), seed packets report germination percentage (typically 75–95%). If you need 200 carrot plants at final spacing and the seed has 85% germination, sow at least 200 ÷ 0.85 = 236 seeds, then thin to final spacing after germination. For expensive or rare seeds, sow at 2–3× the final density and thin; for bulk vegetable seed, sow at 4–5× density and thin after germination.

The soil calculator helps determine how much growing medium is needed to prepare the bed to the correct depth before planting at the calculated spacing, while the plant population calculator provides the complementary calculation for arable and field-scale crops where population per hectare is the primary planning variable.