Vegetable Seed Calculator
Enter your crop type, row length, and number of rows and the calculator tells you how many seeds (and transplant seedlings) you need. It reads the recommended in-row spacing from a built-in table of 35 common vegetables, accounts for germination failure with a configurable buffer, and shows the full working so you can audit every step. Switch between feet and metres for the row length. Add a seed cost per packet to get an instant budget estimate.
How to calculate how many vegetable seeds you need
The core formula is straightforward: divide the row length (in inches) by the recommended in-row spacing for your crop, then floor the result to a whole number. Multiplying by the number of rows gives the total seeds to plant. For example, a 10-foot row is 120 inches. Tomatoes spaced 12 inches apart fit 120 / 12 = 10 per row. Three rows require 30 seeds to plant. That is the figure to use if every seed germinates and survives. In practice, germination rates vary by seed age, soil temperature, and moisture, so most gardeners and commercial growers add a buffer of 10-20% on top, buying enough seeds to cover losses.
Seeds vs. seedlings: which count should you use?
Some crops are almost always direct-seeded: carrots, beets, radishes, peas, and beans grow best when sown straight into the garden. Others, particularly tomatoes, peppers, eggplant, broccoli, and celery, are typically started indoors weeks before the last frost and transplanted as seedlings. This calculator provides both counts. The seedling spacing is wider than the seed spacing for crops like broccoli and tomatoes because indoors you thin or space seedlings before they go in the ground, while direct seeding often relies on post-germination thinning. If you plan to transplant, use the seedling count and the wider spacing to plan your indoor trays. If you will direct-seed and thin, use the seed count and tighter spacing.
Understanding the germination buffer
Seed germination is never 100%. A well-maintained seed packet from a reputable supplier might list 85-90% germination for tomatoes, meaning roughly 1 in 7 seeds will not sprout even under ideal conditions. Older seeds, cold soil, or dry conditions can push the failure rate higher. A 10-15% buffer covers typical losses for fresh, high-quality seed. Boost it to 20-25% for slow or fussy germinators such as parsnip, celery, or carrot seed that has been stored for more than one season. The buffer applies to your buy quantity only: if you plant 30 seeds and want a 15% safety margin, you buy 35 seeds (ceil(30 x 1.15)).
Planning rows and packets
Once you know how many seeds to buy, divide by the packet size to find how many packets to purchase, rounding up. A 10-foot row of carrots at 2-inch spacing holds 60 seeds per row. Two rows need 120 seeds to plant, and 138 with a 15% buffer. A packet of 500 carrot seeds is more than enough for this garden and will keep for 2-3 years in a cool, dry location. Larger vegetable plots may need several packets of the same crop; this calculator rounds up to the nearest whole packet so you always have enough.
Recommended vegetable seed and seedling spacing
| Vegetable | Seed spacing (in) | Seedling spacing (in) |
|---|---|---|
| Artichoke | 24 | 48 |
| Asparagus | 12 | 18 |
| Bean (bush) | 3 | 4 |
| Bean (pole) | 4 | 6 |
| Beet | 2 | 3 |
| Broccoli | 6 | 18 |
| Brussels sprout | 6 | 24 |
| Cabbage | 6 | 18 |
| Cantaloupe | 12 | 24 |
| Carrot | 2 | 3 |
| Cauliflower | 6 | 18 |
| Celery | 4 | 6 |
| Chard (Swiss) | 4 | 6 |
| Corn (sweet) | 9 | 12 |
| Cucumber | 6 | 12 |
| Eggplant | 6 | 18 |
| Garlic | 4 | 4 |
| Kale | 4 | 12 |
| Kohlrabi | 4 | 6 |
| Leek | 3 | 6 |
| Lettuce (head) | 4 | 12 |
| Lettuce (leaf) | 2 | 4 |
| Melon (watermelon) | 12 | 24 |
| Onion | 3 | 4 |
| Parsnip | 3 | 4 |
| Pea | 2 | 3 |
| Pepper | 6 | 18 |
| Potato | 10 | 12 |
| Pumpkin | 12 | 24 |
| Radish | 2 | 2 |
| Spinach | 3 | 4 |
| Squash (summer) | 12 | 24 |
| Squash (winter) | 18 | 36 |
| Tomato | 12 | 24 |
| Turnip | 3 | 4 |
| Zucchini | 12 | 24 |
In-row spacing values from University of California Cooperative Extension and University of Minnesota Extension. Actual spacing varies by variety; consult your seed packet.
Frequently asked questions
Why does the calculator floor the seeds per row instead of rounding normally?
Flooring prevents fractional seeds from accumulating across many rows. If a row holds 7.6 seeds and you round up to 8, then multiply by 10 rows, you get 80 seeds. But you cannot plant 0.6 of a seed in the last slot of any row: each individual row physically fits only 7 plants at the set spacing. Flooring each row to 7 and multiplying by 10 gives 70, which is what the plot will actually hold. The buffer percentage then handles any extra insurance you want to add on top.
What germination buffer percentage should I use?
For fresh seed purchased from a reputable supplier, 10-15% is a reasonable buffer and covers typical germination variability. Use 20-25% for seeds that are more than one season old, crops that are sensitive to temperature (peppers, eggplant, celery), or if you are direct-seeding into cold, wet soil early in spring. If a seed packet lists a tested germination rate below 80%, consider buying extra to compensate: the buffer percentage should be at least (1 / germination_rate - 1) x 100.
Can I use the seedling count for all crops?
The seedling count is most relevant for crops that benefit from indoor starting: tomatoes, peppers, eggplant, broccoli, cauliflower, cabbage, kale, leeks, and celery. Root vegetables such as carrots, parsnips, and radishes do not transplant well because disturbing the taproot stunts them. Legumes (peas and beans) can be transplanted but rarely need to be. For these crops, use the seed count and direct-sow outdoors when soil conditions are right.
How is in-row spacing different from row spacing?
In-row spacing is the distance between plants (or seeds) along the length of one row. Row spacing is the distance between adjacent parallel rows. This calculator handles in-row spacing only because that is what determines how many seeds go into each row. Row spacing affects how many rows fit in your bed width but does not change the seed count per row. For most vegetables, row spacing is 12-36 inches depending on plant size and whether you need to walk between rows.
What if my crop is not in the dropdown?
Select "Custom spacing" at the bottom of the crop list and enter your own seed-to-seed and seedling-to-seedling distances in inches. Check your seed packet or the supplier's catalog for the recommended spacing. University cooperative extension services in your region also publish spacing tables as free guides online.
How many seed packets should I buy?
The calculator divides your seeds-with-buffer by the packet size you enter and rounds up to the nearest whole packet. If you are ordering from a catalog, note that packet sizes vary widely: a "standard" packet of tomato seed might hold 25 seeds, while a carrot packet might hold 500-1000. Always check the seed count on the product listing rather than assuming a standard size.