How the calculation works

The calculator places plants on a grid inside your bed and counts them row by row.

Margin: the outer plants sit a set distance in from the edges; left blank, that is half the spacing. Plant centres go anywhere in what is left: length − 2 × margin by width − 2 × margin.
Square grid: plants per row = (usable length ÷ spacing, rounded down) + 1. The number of rows is worked out the same way across the width. Plants = rows × plants per row.
Staggered (triangular) grid: the rows are spacing × 0.866 apart (√3 ÷ 2) and every other row starts half a spacing further in, so each plant is the same distance from its six nearest neighbours. A shifted row can hold one plant fewer than the others, so the two kinds of row are counted separately. The calculator tries the rows both along and across the bed and uses whichever fits more.
I know the area: plants = area ÷ (spacing × spacing) for a square grid, or area ÷ (spacing × spacing × 0.866) for a staggered one, rounded up. This ignores the edges, so it runs a little high for a small bed.
Units: spacing in inches is divided by 12 to get feet, and centimetres by 100 to get metres.

Worked example

A 4 × 8 ft raised bed of spinach, 6 inches apart, with the margin left blank. The outer plants sit 3 inches in from the edges, so the plant centres fill 90 × 42 inches.

Square grid: 90 ÷ 6 = 15 gaps, so 16 plants per row. 42 ÷ 6 = 7 gaps, so 8 rows. 8 × 16 =128 plants, or 4 per square foot.
Staggered grid: the rows are 6 × 0.866 = 5.2 inches apart, and 42 inches holds 8 of those gaps, so there are 9 rows. Five of them hold 16 plants. The four shifted rows start 3 inches further in, leaving 87 inches: 87 ÷ 6 = 14.5, so 14 whole gaps and 15 plants. 5 × 16 + 4 × 15 = 140 plants, 12 more than the square grid (about 9% more).
From the area alone, a staggered grid would need 32 ÷ (0.5 × 0.5 × 0.866) = 147.8, so 148 plants. The real bed fits fewer because of its edges.

In metric, a 2.4 × 1.2 m bed at 15 cm works out the same way: 128 plants in a square grid (44.4 per m²) or 140 staggered (48.6 per m²).

Why staggered planting fits about 15% more

In a square grid each plant has a square of ground, spacing × spacing. In a staggered grid the rows are only 0.866 × the spacing apart, and every other row is shifted half a spacing, so each plant sits in the gap between two plants of the next row. Every plant is still exactly one spacing from its six nearest neighbours, but it now takes up only 0.866 × spacing × spacing of ground. The same area holds 1 ÷ 0.866 = 1.155 times as many plants: 15.5% more. At 12 inches apart, 100 square feet takes 100 plants in a square grid and 116 staggered (115.5 rounded up), with the rows 10.4 inches apart.

You only get the full gain on a large area. In a bed, the rows and plants that don't quite fit at the edges take part of it back. A 4 × 8 ft bed at 12 inches fits 32 plants either way, and at 24 inches a square grid fits 8 tomatoes while a staggered one fits only 7. The calculator shows the other pattern's total too, so you can see which wins for your bed.

When you mark out a staggered grid, set the rows 0.866 × the spacing apart, not a full spacing, and start every other row half a spacing in. If you shift alternate rows but keep them a full spacing apart, you fit no more than in a square grid, and plants in neighbouring rows end up 1.12 spacings apart instead of one.

Even spacing isn't only about numbers. Virginia Tech's intensive gardening guide recommends spacing plants in a bed so that each one is the same distance from the plants on all sides, which in a bed of more than two rows means staggering the rows. The aim is for leaves to touch at maturity: the nearly solid canopy acts as a living mulch, cutting water loss and weeds, as long as plants aren't so crowded that disease or stunting follows. Illinois Extension recommends a staggered or diamond pattern for ground covers too.

Spacing for vegetables in beds

Picking a vegetable fills in a spacing for beds, where plants are the same distance apart in every direction. The figures come from Colorado State University's Vegetable Planting Guide, which gives one spacing for block-style beds to use both within and between rows, and Virginia Tech's Intensive Gardening Methods. For comparison, the "Single rows" column shows Virginia Tech's spacing for traditional rows, where plants sit closer together in the row but the rows are far apart.

The calculator fills in the smallest of the sources' upper limits, which for most crops is a spacing both accept. Two crops fall outside one source's range. For summer squash, Colorado State gives 36–48 inches and Virginia Tech 18–24, so the calculator fills in 24 inches. For leaf lettuce, Colorado State gives 7–9 inches and Virginia Tech 4–6, so it fills in 6. Type your own spacing if you prefer Colorado State's figure.

Vegetable	Beds: Colorado State	Beds: Virginia Tech	Single rows: Virginia Tech	Calculator fills in
Tomato (staked or caged)	24 in trellised	18–24 in	18–36 in, rows 36–50 in apart	24 in (61 cm)
Pepper	15–18 in	12–15 in	12–24 in, rows 30–36 in apart	15 in (38 cm)
Eggplant	18–24 in	18–24 in	18–24 in, rows 30–42 in apart	24 in (61 cm)
Broccoli	18 in	12–18 in	12–24 in, rows 18–36 in apart	18 in (46 cm)
Cabbage	18 in	15–18 in	12–18 in, rows 18–36 in apart	18 in (46 cm)
Cauliflower	18 in	15–18 in	12–24 in, rows 24–36 in apart	18 in (46 cm)
Kale	Not listed	15–18 in	12–24 in, rows 18–36 in apart	18 in (46 cm)
Lettuce, leaf	7–9 in	4–6 in	Not listed	6 in (15 cm)
Lettuce, head	Not listed	10–12 in	6–10 in, rows 10–18 in apart	12 in (30 cm)
Spinach	4–6 in	4–6 in	4 in, rows 6–12 in apart	6 in (15 cm)
Swiss chard	7–9 in	6–9 in	6–12 in, rows 18–30 in apart	9 in (23 cm)
Beets	4–6 in	2–4 in	2–3 in, rows 12–18 in apart	4 in (10 cm)
Carrots	2–3 in	2–3 in	1.5–2 in, rows 6–12 in apart	3 in (8 cm)
Radishes	2–3 in	2–3 in	0.75–1 in, rows 6–12 in apart	3 in (8 cm)
Onions (bulb)	4–6 in	2–4 in	2–4 in, rows 12–18 in apart	4 in (10 cm)
Beans, bush	6 in (listed as snap beans)	4–6 in	1–3 in, rows 24–36 in apart	6 in (15 cm)
Peas	4–6 in	2–4 in	2–3 in, rows 12–30 in apart	4 in (10 cm)
Potatoes	12–15 in	10–12 in	10–18 in, rows 24–42 in apart	12 in (30 cm)
Summer squash	36–48 in	18–24 in	18–36 in, rows 36–60 in apart	24 in (61 cm)

Colorado State says to use the closer spacings in its ranges only on improved soils with 4–5% organic matter.
Colorado State suggests beds 2–4 ft wide with 2 ft paths between them. Virginia Tech says beds are generally 3–4 ft wide, so you can work from either side without walking on the soil.
Virginia Tech's row guide suggests spacing plants closer together in the row when the rows are farther apart, and farther apart in the row when the rows are closer together.
Metric figures are the inch figures converted and rounded to the nearest centimetre.

Ground covers and bedding plants

The ground cover choices in the calculator are common spacings from 6 to 24 inches (15 to 60 cm), not advice for a particular plant. How far apart to plant depends on the plant:

Illinois Extension says spacing depends on the plant's habit, how fast it grows, cost and how quickly the area needs covering, and to space faster-growing ground covers farther apart than slow ones. It suggests allowing at least one to two growing seasons for a planting to become completely established.
Virginia Tech notes that a wider spacing means fewer plants, so less cost and planting work, but a slow grower planted far apart leaves open soil where weed seeds can sprout.
Illinois Extension's chart of plants needed for an area is worked out like a square grid: 100 square feet at 12 inches takes 100 plants. If you set staggered rows 0.866 × the spacing apart, buy about 15% more.

For bedding plants, use the spacing on the plant tag or seed packet.

Common questions

How many plants fit in a 4 × 8 ft raised bed?: It depends on the spacing. With the outer plants half a spacing in from the edges, a 4 × 8 ft bed holds 128 plants at 6 inches apart (140 staggered), 32 at 12 inches (also 32 staggered), 10 at 18 inches (12 staggered) and 8 at 24 inches (only 7 staggered). In a square grid that is 4, 1, 0.31 and 0.25 plants per square foot.
How many ground cover plants do I need for 100 square feet?: In a square grid you need 400 plants at 6 inches apart, 225 at 8 inches, 100 at 12 inches and 45 at 18 inches, the same figures as University of Illinois Extension's chart. Illinois recommends planting ground covers in a staggered or diamond pattern. With staggered rows set 0.866 × the spacing apart, the same area takes about 15% more plants: 462, 260, 116 and 52. In metric, 10 m² at 30 cm needs 112 plants in a square grid or 129 staggered.
What does the edge margin do?: It sets how far the centres of the outer plants sit from the edge of the bed. Leave it blank and the calculator uses half the spacing, so a circle one spacing across around each plant stays inside the bed: a 4 × 8 ft bed at 12 inches then fits 32 plants. With a margin of 0, plants go right on the edge and the same bed fits 45 (5 rows of 9), but the outer plants hang half over the side. A wider margin keeps plants back from a path or a wooden frame.
Is the spacing on a seed packet the right spacing for a bed?: Check it against a bed guide. Virginia Tech's intensive gardening guide explains that the in-row spacing on a seed packet is measured from the centre of one plant to the centre of the next, and that in a bed each plant should be the same distance from the plants on all sides. Row and bed figures don't always match, though. For beets, Virginia Tech's row guide gives 2–3 inches apart in rows 12–18 inches apart, its intensive guide gives 2–4 inches for beds, and Colorado State's bed guide gives 4–6 inches in every direction. Pick a vegetable in the calculator to see both universities' bed spacing.

Sources

Last checked and updated: October 31, 2026.