How it works
The calculator divides the planted area by the area each plant takes up, or divides a row into equal spaces.
Planted area = (Length − 2 × Setback) × (Width − 2 × Setback)
Square grid: Plants = ⌈ Planted area ÷ Spacing² ⌉
Offset rows: Plants = ⌈ Planted area ÷ (0.866 × Spacing²) ⌉, rows 0.866 × Spacing apart
Single row: Plants = ⌊ (Row length − 2 × Setback) ÷ Spacing ⌋ + 1
⌈ ⌉ means rounding up to a whole plant, ⌊ ⌋ rounding down. 0.866 is sin 60° (√3 ÷ 2): in offset rows each plant sits at the corner of an equilateral triangle, so the rows close up to 0.866 of the spacing. That is why University of Georgia Extension’s table lists 462 plants per 100 sq ft at 6 in in a triangular pattern against 400 in a square one. Units are converted internally, so a bed in feet with a spacing in inches, or meters and centimeters, works directly.
Worked example
Inputs
- Planting
- Bed, length × width
- Bed length
- 10 ft
- Bed width
- 5 ft
- Pattern
- Offset rows (triangular)
- Spacing between plants
- 12 in
- Edge setback
- 0 in
Result
- Plants needed
- 58
- With the other pattern
- 50
- Distance between rows
- 10.39 in (0.866 ft)
- Area per plant
- 0.866 sq ft
- Area planted
- 50 sq ft
Common mistakes
- Using the plant’s mature width as the spacing for groundcovers. Groundcovers are set closer so they meet in a season or two; use the spacing your extension service or the plant tag gives.
- Spacing offset rows as far apart as the plants. In a triangular pattern the rows are only 0.866 × the spacing apart – rows set a full spacing apart leave gaps.
- Forgetting the units. A 12 in spacing is 1 ft; entering 12 ft by mistake gives 144 times fewer plants.
- Planting right up to a wall or path. Leave an edge setback so plants have room to spread without hanging over.
Assumptions and limits
- The bed is a rectangle, or you have entered its total area, and the spacing is the same in every direction.
- Plants in a bed are counted by area – the planted area divided by the area each plant gets – and rounded up. A real layout can need a plant or two more or fewer where rows meet the edges.
- The edge setback is taken off every side of a bed (length × width only) and off both ends of a row.
- A single row has a plant at each end. Double or staggered rows can be entered as a bed.
Frequently asked questions
How many plants do I need for 100 square feet?
At 12 in spacing, 100 plants in a square grid or about 116 in offset rows; at 6 in spacing, 400 or 462. University of Georgia Extension’s planting table gives the same counts (it rounds 115.5 to 115).
How do I calculate plant spacing in a triangular pattern?
Each plant takes up 0.866 × spacing × spacing, so divide the bed area by that figure. The rows are 0.866 × the spacing apart and every other row is shifted half a spacing. Compared with a square grid, divide by 0.866 – about 1.155 times as many plants.
Square or triangular spacing – which is better?
Offset (triangular) rows cover the ground more evenly and are common for groundcovers and mass plantings; a square grid is easier to lay out and needs fewer plants at the same spacing. The calculator shows both counts.
How many plants fit in a row?
Divide the row length by the spacing, round down and add one for the plant at the start. A 20 ft row at 18 in spacing holds 240 ÷ 18 = 13.3 → 13 + 1 = 14 plants.
What spacing should I use?
It depends on the plant, its mature size and how quickly you want the bed to fill. Use the spacing on the plant tag or ask your local extension service; this calculator only does the counting.
Sources
- Conversion Tables, Formulas and Suggested Guidelines for Horticultural Use (Bulletin 931), Table 31 — University of Georgia Cooperative Extension. Plants to fill 100 sq ft: square spacing (rows as far apart as the plants) 900 / 400 / 225 / 144 / 100 / 74 at 4–14 in; triangular (equilateral) spacing with rows 3.46 / 5.20 / 6.93 / 8.66 / 10.39 / 12.12 in apart, 1,039 / 462 / 260 / 166 / 115 / 85 plants. The row distances are 0.866 × the spacing (the text prints "0.886 X").
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 6, 2026