Seed Quantity Calculator: How Many Seeds to Sow
Choose a bed area or a single row, enter how far apart you want plants, then add the germination rate printed on the packet and a safety margin for failures. The result is the seeds to sow and the packets to buy. After switching units, re-enter your measurements.
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Formula
- By area:
positions = area / (seed spacing x row spacing) - By row:
positions = row length / seed spacing seeds = positions / germination rate x (1 + safety margin)packets = seeds / seeds per packet, always rounded up
Worked example
100 ft2 of bed, seeds 6 in apart in rows 12 in apart (cell = 0.5 ft2), 80% germination, 20% safety margin, 50 seeds per packet:
- 100 / 0.5 = 200 positions
- 200 / 0.80 = 250 seeds; x 1.20 = 300 seeds
- 300 / 50 = 6 packets
Row version: a 25 ft row with seeds 3 in apart has 300 / 3 = 100 positions; at 80% germination and 0% margin that is 125 seeds.
When to use it
Use it before you shop, so you buy enough packets for a bed or a row without paying for far more than you need. Germination and spacing figures printed on packets are typical values for fresh seed. If the packet is a year or two old, lower the germination rate.
Common mistakes
- Using the spacing between plants as the row spacing, or the other way round.
- Skipping the safety margin outdoors, where cold soil, birds and slugs take their share. A margin of 10 to 30 percent is typical.
- Forgetting that crops sown thickly and thinned need more seeds than this tool shows.
- Entering the row length in inches when the unit is feet.
How it differs from nearby calculators
The germination rate calculator measures a rate from a seed test or tells you the seeds for a given number of plants. The plant spacing calculator counts the plants a bed holds, while this one converts that count into seeds and packets. The garden bed area calculator measures the bed first.
Frequently asked questions
How many seeds do I need for 100 square feet?
With seeds 6 inches apart in rows 12 inches apart, each plant takes 0.5 square foot, so 100 square feet has 200 positions. At 80 percent germination that is 200 / 0.8 = 250 seeds, and a 20 percent safety margin makes 300. In packets of 50 that is 6 packets.
What is the germination rate?
It is the share of seeds expected to sprout, usually printed on the packet. A rate of 80 percent means about 8 in 10 seeds germinate. Old seed germinates less well, so lower the rate if your packet is a year or two old.
Why add a safety margin?
Germination rates come from lab tests. Cold soil, birds, slugs and uneven watering lose more seeds outdoors, so a margin of 10 to 30 percent is a typical allowance. It is not a rule; use 0 if you will sow indoors and thin or transplant.
How many seeds for a single row?
Divide the row length by the seed spacing, then correct for germination. A 25 foot row (300 inches) with seeds 3 inches apart has 100 positions. At 80 percent germination and no extra margin, sow 125 seeds. Tiny seeds such as carrots are usually sown thickly and thinned, so this is a lower bound.
How many carrot seeds do I need for a 10 foot row?
A 10 foot row is 120 inches. At 2 inch spacing that is 60 positions, and at a germination rate of 70 percent with no safety margin you need 60 / 0.7 = 86 seeds, which is 2 packets of 50. Carrots are often sown thicker and thinned, so this is a lower bound.
How many seeds for a 4x8 bed with 12 inch spacing?
The bed is 32 square feet and each plant takes 1 square foot, so there are 32 positions. At 80 percent germination and a 20 percent margin you need 32 / 0.8 x 1.2 = 48 seeds, which is one packet of 50.
How many seeds for 10 square metres in metric units?
Use metric mode with seeds 10 cm apart in rows 30 cm apart. Each plant takes 300 cm2, so 10 m2 has 334 positions. At 90 percent germination and a 10 percent margin that is 409 seeds, or 5 packets of 100.