How Many Seeds per Square Meter? Calculator + Density Table
Knowing how many seeds per square meter to sow is the single most important number before you buy seed packets. Sow too few and you get bare patches; sow too many and plants compete for light and water, producing stunted, low-quality crops. This calculator gives you the answer instantly: enter your garden area and select your crop. The formula is simple: Seeds needed = Area (m²) × Seed density (seeds/m²) Then add 15–20 % extra to cover seeds that fail to germinate — field germination rates typically run 70–85 %, even for fresh commercial seed. ## Seed density table by crop | Crop | Seeds/m² (sowing) | Final plants/m² | Germination rate | |---|---|---|---| | Carrot | 200 | 80–100 | 65–75 % | | Radish | 110 | 80–100 | 80–90 % | | Spinach | 100 | 60–80 | 60–70 % | | Lettuce | 60 | 16–25 | 75–85 % | | Tomato (tray) | 10 | 3–4 | 80–90 % | Reference values per USDA Cooperative Extension and RHS growing guides. For tomatoes, the density shown is for seedling trays — you sow 2 seeds per cell, thin to the strongest, then transplant at ~3–4 plants/m² in the final bed.
Seeds needed = garden area (m²) × seed density for the crop. Key densities: carrot 200 seeds/m², radish 110 seeds/m², spinach 100 seeds/m², lettuce 60 seeds/m², tomato (seedling tray) 10 seeds/m². For a 10 m² carrot patch: 10 × 200 = 2,000 seeds. Always sow 15–20% extra to compensate for germination failures.
When to use this calculator
- Planning a 10 m² backyard carrot bed: 10 × 200 = 2,000 seeds, plus 15% buffer = 2,300 seeds — one standard commercial packet (typically 1,000–5,000 seeds per 5 g).
- Sizing a 5 m² lettuce plot: 5 × 60 = 300 seeds, plus 20% buffer = 360 seeds, roughly one small foil packet.
- Starting tomato seedlings for a 20 m² final bed: 20 × 3.5 final plants = 70 plants needed; at 85% germination, sow 83 seeds in trays — easily covered by a standard 0.2 g packet (≈ 60 seeds) plus one extra packet.
- Setting up a 12-plot community garden (3 m² each): calculate seed needs per species across 36 m² total area before bulk-ordering.
- Comparing seed quantity to packet weight when labels show grams instead of seed count — knowing the seeds-per-gram figure for each species.
- Teaching school children practical math: compute seed requirements for a 5 m² school garden plot using multiplication and percentages.
- Planning succession sowings of radish every 2 weeks in a 2 m² strip: each sowing = 2 × 110 = 220 seeds, budget for 6–8 sowings per season.
- Stretching a limited gardening budget by ordering exact quantities rather than buying excess packets whose viability drops after 2–3 years of storage.
Worked example — 10 m² carrot patch
- Area = 10 m²
- Carrot density = 200 seeds/m²
- Seeds needed = 10 × 200 = 2,000
- Add 15% for germination failures: 2,000 × 1.15 = 2,300 seeds
How it works
2 min readHow the calculation works
The formula multiplies your sowing area by the recommended seed density for that crop:
Seeds = Area (m²) × Density (seeds/m²)To account for germination losses, add 15–20 % on top:
Seeds to buy = Seeds × (1 + germination buffer)
= 2,000 × 1.15 = 2,300 [carrot, 10 m²]Density values used in this calculator
| Crop | Seeds/m² | Why |
|---|---|---|
| Carrot | 200 | Small seed, later thinned to 80–100 plants/m² at 5×2 cm |
| Radish | 110 | Fast cycle (25–35 days), thin to 80/m² at 5×5 cm |
| Spinach | 100 | Thin to 60–80 plants/m² at 8×10 cm spacing |
| Lettuce | 60 | Head varieties thinned to 16–25/m²; baby-leaf up to 80–100/m² |
| Tomato | 10 | Seedling trays only — 2 seeds/cell, transplant at 3–4 plants/m² |
Why germination rate matters
Commercial seed packets guarantee 80–90% germination under lab conditions. In real garden beds, you should plan for 65–85 % depending on soil temperature, moisture and seed age. Old or improperly stored seeds can drop to 40–50 %. A simple viability test: place 10 seeds on a damp paper towel in a sealed bag for 7–10 days — if 7 germinate, you have 70 % viability and should sow ~43 % more seeds.
Comparing seed packet weights to seed counts
Packets usually show weight, not count. Approximate seeds per gram:
| Crop | Seeds/gram |
|---|---|
| Carrot | 700–1,000 |
| Lettuce | 700–1,000 |
| Radish | 80–120 |
| Spinach | 80–100 |
| Tomato | 250–350 |
So a 5 g carrot packet contains roughly 3,500–5,000 seeds — enough for 17–25 m² at 200 seeds/m².
Thinning: from seeds to final plants
You always sow more seeds than you want as mature plants, then thin the excess:
For lettuce and spinach, thinnings are edible — use them in salads.
Frequently asked questions
How many seeds per square meter for carrots?
Sow 200 carrot seeds per square meter for direct sowing, then thin to 80–100 mature plants/m² (roughly 5 × 2 cm spacing). Carrot seeds are tiny (≈ 0.8 mg each), so a standard 5 g packet contains 3,500–5,000 seeds — enough for 17–25 m². Use the calculator above to get the exact count for your patch size.
How many seeds per square meter for lettuce?
Sow 60 lettuce seeds per square meter for head varieties, thinning to 16–25 final plants/m² at 25–30 cm spacing. For baby-leaf (cut-and-come-again) production, increase to 80–100 seeds/m². Lettuce has around 800–1,000 seeds per gram, so even a small 1 g packet covers 13–16 m².
How many seeds per square meter for spinach?
Sow 100 spinach seeds per square meter, thinning to 60–80 plants/m² at 8 × 10 cm. Spinach has one of the lowest germination rates of common vegetables (60–70 %), so sowing at 100/m² compensates and gives you enough to thin. A standard 10 g packet (≈ 800–1,000 seeds) covers 8–10 m².
How many seeds per square meter for radishes?
Sow 110 radish seeds per square meter, thinning to 80–100 plants/m² at 5 × 5 cm. Radishes germinate fast (3–5 days) and have an 80–90 % germination rate, so losses are low. A 5 g packet (≈ 400–600 seeds) covers roughly 4–5 m².
How many seeds per square meter for tomatoes?
Tomatoes are almost always started in seedling trays rather than direct-sown. Use 10 seeds per square meter of tray area, sowing 2 seeds per cell and thinning to the strongest. The final planting density in the garden bed is 3–4 tomato plants per square meter (50–70 cm spacing). One standard 0.2 g packet (≈ 60–70 seeds) is enough for 6–7 m² of tray.
Should I direct-sow or start transplants indoors?
Direct sow: crops that dislike root disturbance — carrots, radishes, spinach, beets, parsnips. Sow seeds straight into the final bed. Start indoors as transplants: warm-season crops (tomatoes, peppers, eggplants) that need a long growing season. Start 6–8 weeks before last frost, then transplant when soil temperature exceeds 15°C. Either method works: lettuce, kale, chard — direct sowing is cheaper; transplants give a 4–6 week head start.
How do I test whether my old seeds are still viable?
Place 10 seeds on a damp paper towel, fold, seal in a plastic bag and leave at room temperature for 7–10 days. Count how many germinate. If 8 of 10 sprout, you have 80% viability and the standard sowing density is fine. If only 5 sprout (50%), sow 2× the normal density. Expected viability by age (cool dry storage): lettuce/tomato/radish 4–6 years; spinach/beet/peas 3–4 years; carrot/parsley 1–3 years; onion 1–2 years.
What planting depth is correct for each crop?
General rule: plant seeds at 2–3× their own diameter. Carrot: 0.5–1 cm (tiny seeds — barely cover with fine soil). Radish: 1–2 cm. Spinach: 1.5–2 cm. Lettuce: 0.5 cm or press onto surface. Tomato (tray): 0.5–1 cm. Planting too deep is the #1 cause of poor germination in small-seeded crops — the seedling runs out of energy before reaching light.
Can I apply these seed densities to raised beds and containers?
Yes — the seeds-per-square-meter figures apply equally to raised beds, in-ground plots and large containers. The planting area is what matters, not the structure around it. For containers smaller than 0.5 m² (e.g. a 30 × 30 cm pot), just scale down: 0.09 m² × 200 seeds/m² = 18 carrot seeds in that pot. Square-foot gardening grids translate directly — 1 square foot ≈ 0.093 m².
How long will unused seeds stay viable?
Stored in a cool (5–15°C), dry, dark place: lettuce, tomato, radish, brassicas = 4–6 years; spinach, beet, peas, beans = 3–4 years; carrot, parsley, parsnip = 1–3 years; onion, leek, sweet corn = 1–2 years. Sealed in an airtight container with a silica-gel packet in a refrigerator, viability extends further. Always label packets with species, variety and harvest or purchase year.