Plant Spacing Calculator

How the Plant Spacing Calculator Works

The calculator uses a mathematical grid model — the same approach used in commercial horticulture and square foot gardening — to count how many planting positions fit within a given area at your chosen spacing. Choose the layout mode that matches how you plan to plant, and the calculator handles the geometry automatically.

Grid Layout — Square-Grid Planting

Grid Layout places plants in a square grid where the same spacing interval applies in both the length and width directions. This mode is suited to intensive beds of compact crops — lettuce, herbs, beetroot, spinach, radish — where equal spacing in all directions maximises yield per square metre. The total plant count is: plants per row × number of rows, where plants per row = floor(bed length ÷ spacing) + 1 and number of rows = floor(bed width ÷ spacing) + 1.

Row Planting — Separate Plant and Row Spacing

Row Planting uses two different spacing values: plant spacing (the gap between plants within a row, along the bed length) and row spacing (the gap between rows, across the bed width). This reflects how most vegetable gardeners actually plant — tomatoes at 60 cm within a row, rows 90 cm apart; or carrots 8 cm apart in a row with rows 20 cm apart. The wider row spacing provides access between rows and allows air to circulate between the canopy layers, reducing disease pressure on crops like brassicas and solanums.

Single Row — One Line of Plants

Single Row mode calculates plants along a single straight line of any length. Enter the row length and plant spacing; the result is floor(length ÷ spacing) + 1. This mode is useful for border plantings, hedge rows, and container edges, or when planning beds one row at a time before combining rows manually. If you are planting multiple parallel rows of equal length, enter the row count to get a total plant figure across all rows.

Container — Circular and Rectangular Raised Beds

Container mode calculates plants in a round circular bed or a rectangular raised container. For a rectangular container, the calculation is identical to Grid or Row Planting but scoped to the container dimensions. For a round circular bed, the calculator iterates a square grid from the centre outward and counts all positions within the circle radius — producing a result that accounts for the curved edges where the grid extends beyond the circle boundary. A 120 cm diameter circular bed with 30 cm spacing, for example, holds 13 plants rather than the 25 a full 4×4 square grid of the same span would suggest.

Plant Spacing Formula

The calculator uses a simple counting formula applied to each dimension independently. All spacing values are converted to centimetres internally before the calculation, regardless of the unit system selected.

Plants per Row Formula

The number of plants that fit along a single straight line is:

Where:

• Length = the distance available for planting (bed length or row length, in cm)
• Spacing = the gap between adjacent plants (in cm)
• floor( ) = round down to the nearest whole number
• The + 1 accounts for the plant at position zero (the starting edge)

The calculator handles this calculation automatically — the formula is shown here for transparency.

Circular Bed Formula

For a round bed of diameter D, the calculator places a square grid with the given spacing, centred on the bed midpoint, and counts all grid positions where the distance from the centre is less than or equal to the radius (D ÷ 2). Positions on the edge are included; positions outside are excluded.

Plant Spacing Chart — Common Vegetables and Flowers

The table below shows recommended final spacings for 15 common garden crops. These are the spacings for transplants or thinned seedlings at full size — not sowing distances. Enter these values into the calculator to get your plant count for any bed size.

The 4×8 ft plant counts are calculated using the Row Planting formula on a 122 × 244 cm bed. For soil volume calculations for the same bed, use our Raised Bed Soil Calculator.

What Your Plant Count Means

The total plant count tells you how many planting positions exist at your chosen spacing — but interpreting that number in context helps you plan your growing season more effectively.

1–5 plants — a very wide-spaced planting of large, spreading crops. Courgettes (1 plant per 0.81 m²), established climbing roses, and large heritage tomatoes fall here. A 4×8 ft bed holds 4 courgettes at most before competition for water and light significantly reduces yield per plant. If your count is this low, verify the spacing is correct — a common mistake is entering centimetres when the preset shows inches.

6–20 plants — medium crops at recommended spacing. Tomatoes, peppers, cabbages, cucumbers, and most brassicas fall in this range for a standard raised bed. This count reflects a well-planned productive bed with good airflow between plants and clear row access for harvesting and maintenance.

21–100 plants — intensive planting of compact or cut-and-come-again crops. Lettuce, spinach, onion sets, herbs, and French marigolds fill this range for most raised bed sizes. At this density, consistent feeding and watering becomes critical, as root competition increases after canopy closure at 4–6 weeks post-planting.

Over 100 plants — fine-spaced crops typically grown from direct seed and thinned to final spacing. Carrots, beetroot, radish, and peas commonly produce counts in the hundreds for a standard bed. Note that this calculator shows your final thinned count, not the number of seeds to sow. Sow at two to three times this density and thin progressively as seedlings develop.

Planting Tips to Get the Most from Your Spacing

• Start plants at the bed edge, not half a spacing in — this calculator places the first plant at position zero (the edge) and the last plant at the far end. If you prefer to offset the first plant half a spacing from the edge (a common practice for a neater look), reduce your bed length and width by one spacing before entering values. This will reduce the count by one plant per row.
• Use the Row Planting mode for most vegetables — even when rows look like a square grid, most vegetable spacings call for a wider row spacing than plant spacing. Using separate values for each gives a more accurate count and reflects how seeds and transplants are actually managed on seedbed equipment and planting benches.
• Thinning crops: calculate final spacing, not sowing spacing — for direct-sown crops such as carrots, beetroot, and radishes, the plant count this calculator produces is the number of plants after thinning, not the number of seeds to sow. Sow at two to three times the final density to ensure a full stand, and thin progressively to the target spacing.
• Companion planting does not change the per-crop count — if you are interplanting marigolds between tomatoes, calculate each crop's plant count separately using its own spacing, and then combine the totals. Do not adjust spacing to accommodate companions — each crop still needs its full recommended space for root and canopy development.
• Succession planting extends your harvest without increasing bed count — rather than planting all positions at once, plant one third of your calculated count every 2–3 weeks. For a bed of 65 lettuces, three plantings of 22 seeds at 3-week intervals gives a 9-week harvest window from a single bed. Use our Potting Soil Calculator to plan soil volume for repeated sowing trays.
• Raised bed edges extend usable growing space — plants within 10–15 cm of a timber or brick raised bed wall experience less root competition from adjacent plants and can tolerate being placed at slightly tighter spacing than the open-ground recommendation. However, the calculator uses standard spacing for all positions; treat the extra edge tolerance as a buffer rather than a reason to reduce spacing across the whole bed.