Plant Spacing Calculator

What the plant spacing calculator does

When you are filling a bed with plants set a fixed distance apart, working out how many you need by hand is fiddly, and guessing means a second trip to the nursery or a tray left over. This works it out. You give it the size of the bed and the spacing between plants, and it returns how many plants fit, worked out two ways, along with the total area.

The two ways are the square and triangular layouts, and the difference between them is worth understanding, since one fits more plants than the other. Below is how it works.

How to use it

1. Enter the area length and width. The size of the bed, each with its own unit.
2. Enter the plant spacing. The distance you want between plants, centre to centre, with its unit.
3. Pick the area unit you want the total shown in, then press Calculate, or Reset to clear it.

How the plant count is worked out

For a square layout, plants sit in straight rows and columns, so the count is just how many fit along the length times how many fit across the width:

Plants = (length ÷ spacing) × (width ÷ spacing)

Each of those divisions is rounded down, since a part of a space cannot hold a whole plant. The triangular layout uses the same idea but with the rows nudged closer together, which is the part worth a proper look in the next section. The calculator works both out and shows you each, plus the total area of the bed.

Square versus triangular spacing

In a square layout, every plant sits directly behind the one in front, so the bed is a neat grid of rows and columns. In a triangular layout, every other row is shifted across by half a space, so each plant nestles into the gap between two in the row ahead. It is the pattern you see in a well-planted orchard.

Here is the useful part. When you stagger the rows like that, the rows themselves can sit closer together while keeping every plant the same distance from its neighbours. Closer rows mean more rows fit, so a triangular layout packs in roughly 15 percent more plants than a square one in the same bed, for the same spacing. The row spacing works out to the plant spacing times about 0.87, which is where that extra fit comes from. If you want maximum coverage, a ground cover for instance, triangular wins. If you want tidy rows you can walk between, square is easier to manage.

A worked example: a 10 ft by 10 ft bed

Say you are planting a 10 foot by 10 foot bed with plants spaced 12 inches apart.

In a square layout, that is 10 plants along each side, so 10 × 10 = 100 plants. In a triangular layout, the rows tuck closer together, fitting about 11 rows, so you get roughly 110 plants in the same bed.

That extra ten plants for the same spacing is the staggered pattern at work, and it adds up fast over a large bed.

Choosing the right spacing

The spacing you enter is what drives everything, so it is worth getting from the plant rather than guessing. The right distance is usually the mature spread of the plant, so that grown plants just touch and cover the ground without crowding each other. Plant tags and seed packets nearly always give this figure.

Spacing too tight looks full at first but leads to crowding, poor airflow, and competition as the plants grow. Spacing too wide leaves bare gaps and lets weeds in. Matching the spacing to the mature size is what gives even, healthy cover, and this calculator then turns that distance into a count.

Questions people ask

How many plants do I need?

Enter the bed size and the spacing, and the calculator gives the count for both a square and a triangular layout. A 10 by 10 foot bed at 12 inch spacing fits about 100 plants in a square grid, or 110 triangular.

Why does the triangular pattern fit more plants?

Because staggering every other row lets the rows sit closer together while keeping plants the same distance apart. More rows fit, so you get roughly 15 percent more plants.

Which spacing pattern should I use?

Triangular for the most plants and fullest cover, like a ground cover. Square for tidy rows that are easier to walk between and maintain.

What spacing should I use?

Usually the mature spread of the plant, so grown plants just meet without crowding. The figure is nearly always on the plant tag or seed packet.

References

A quick note on the numbers. Both plant counts are pure geometry: a square grid is simply rows times columns, and the triangular grid uses a row spacing of the plant spacing times the square root of 3 over 2, which is about 0.87, the standard result for staggered rows. The unit conversions follow the US National Institute of Standards and Technology guide.

1. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811