Plant Spacing Calculator

How many plants actually fit in a raised bed

Nurseries sell plants by the tray, not by the bed. The gap between "I have a 10 by 4 foot bed" and "I need this many six-packs of lettuce" is one piece of arithmetic, and getting it wrong costs money in both directions: buy too few and you make a second trip, buy too many and you crowd the bed into a mildew farm. This calculator turns bed size plus the spacing printed on the tag into a plant count, a row-by-row layout you can mark out with string, and a density figure you can sanity-check against experience.

Worked example: a 10 ft × 4 ft bed at 12 in spacing

Convert everything to inches first: the bed is 120 in long and 48 in wide. With the edge-gap option on, the tool reserves half a spacing (6 in) at each end, so the usable run is 120 − 12 = 108 in. Dividing by 12 gives 9 gaps, and 9 gaps means 10 plants across. The same logic across the width gives (48 − 12) ÷ 12 = 3 gaps, so 4 rows. Ten columns × four rows = 40 plants, or exactly 1.0 per square foot.

Turn the edge gap off and the plants sit right on the bed edges instead: 120 ÷ 12 = 10 gaps = 11 columns, and 48 ÷ 12 = 4 gaps = 5 rows, for 55 plants. That is a 38% jump from one checkbox, which is why the setting matters more than most gardeners expect. Keep the gap on for anything leafy that flops over the frame, turn it off when the bed is bordered by a path you can harvest from.

The same bed, triangular spacing

In a triangular (offset) layout each row is shifted half a space sideways, so rows can sit closer without any two neighbours ending up nearer than the spacing you asked for. The row gap becomes spacing × 0.866 — the height of an equilateral triangle with sides of 12 in, which is 10.39 in. On this bed, (48 − 12) ÷ 10.39 gives 3 gaps, so still 4 rows: the width is too narrow for the tighter rows to buy an extra one. The offset rows also lose one plant each (9 instead of 10), so the total lands at 2 × 10 + 2 × 9 = 38 plants — slightly fewer than the square grid.

Widen the bed to 10 ft × 10 ft and the picture flips. The square grid gives 10 × 10 = 100 plants; the triangular layout fits 11 rows (108 ÷ 10.39 = 10.4 gaps) alternating 10 and 9 plants, for 105. On a field-sized planting the gain converges on the theoretical 15.5% (1 ÷ 0.866), because edge effects stop mattering. The rule of thumb: triangular spacing pays off on wide beds and open ground, and is roughly neutral on a narrow bed. It still closes the canopy faster, which suppresses weeds and keeps soil moisture in.

Square foot gardening in one table

Mel Bartholomew's method is the same maths rounded to whole squares. Each square foot holds a whole number of plants, which maps directly onto spacing:

The calculator does not round to whole squares, so it also handles the awkward numbers the method skips — 8 in for kale, 10 in for bush courgette, 18 in for a determinate tomato — and beds that are 3 ft 6 in wide rather than a tidy 4 ft.

Spacing versus thinning

Direct-sown seed is a different job from transplants. You sow thickly, then thin to the final spacing once the seedlings have their first true leaves. So use the final spacing here to get your plant count, then buy seed by the packet rather than by the plant: a carrot packet holds hundreds of seeds and you will thin most of them out. For transplants — module-raised brassicas, bought six-packs, plug plants — the number this tool gives is exactly what you buy, plus perhaps 10% for losses to slugs and transplant shock.

What this calculator does not know

It assumes a rectangle, flat ground and one crop. It does not account for a trellis line down the middle, the shaded strip along a north fence, paths you need for access, or plants that need staking room. It also treats spacing as a hard minimum, when in reality vigorous soil and generous watering let you push closer while poor dry soil demands more. Treat the result as the planting plan you mark out with string, then adjust by eye for the bed you actually have.