Proper plant spacing prevents overcrowding and maximizes yield. Plants per row = row length in feet × 12 ÷ spacing in inches. For a 10-foot row at 6-inch spacing, that's 20 plants. Multiply by the number of rows for the total seed or transplant order.
The formula
plants per row = floor(row_length_ft × 12 ÷ spacing_in)
total plants = plants_per_row × number_of_rows
The floor() function rounds down — you can't fit a fraction of a plant in the remaining space at the end of a row.
Practical examples
Example 1: Tomatoes at 24-inch spacing in three 8-foot rows (8 × 12 ÷ 24) × 3 = (96 ÷ 24) × 3 = 4 × 3 = 12 plants total
Example 2: Carrots at 3-inch spacing in five 20-foot rows (20 × 12 ÷ 3) × 5 = 80 × 5 = 400 seeds (plant at close spacing and thin later)
Example 3: Corn at 12-inch spacing in six 25-foot rows (25 × 12 ÷ 12) × 6 = 25 × 6 = 150 seeds — add 10–15% extra to account for germination rate
Common mistakes
Using spacing as the distance from the row edge. Spacing is measured center-to-center between plants, not from the edge of the bed. The first plant sits at the spacing distance from the start of the row, not at position zero.
Forgetting germination rate for direct seeding. This calculator gives the number of plants at their final spacing. If direct seeding, order 10–25% more seeds than the total to account for germination failures and thinning.
Applying transplant spacing to seed depth. Final spacing applies to mature plants, not seed depth. Carrot seeds may be dropped every inch and thinned to 3 inches; the spacing in this tool represents the final thinned spacing.
International and regional variations
| Vegetable | US spacing (in) | Metric equivalent (cm) | Notes |
|---|---|---|---|
| Lettuce | 6–8 in | 15–20 cm | Head lettuce needs more space than leaf |
| Tomatoes | 18–24 in | 45–60 cm | Indeterminate varieties need full 24 in |
| Corn | 12 in | 30 cm | Plant in blocks, not single rows, for pollination |
| Carrots | 2–3 in | 5–8 cm | Thin after germination |
| Peppers | 12–18 in | 30–45 cm | Closer spacing in hot climates for shade |
Quick reference
| Spacing (in) | Plants per 10 ft row | Plants per 20 ft row |
|---|---|---|
| 3 | 40 | 80 |
| 6 | 20 | 40 |
| 9 | 13 | 26 |
| 12 | 10 | 20 |
| 18 | 6 | 13 |
| 24 | 5 | 10 |
| 36 | 3 | 6 |
For USDA zone temperature ranges and frost date windows to help plan your planting calendar, see the USDA Plant Hardiness Zone Reference Chart →.