How do I find my germination rate?

Most seed packets print a germination percentage, often from a lab test. To check older seed yourself, place ten seeds on a damp paper towel, keep them warm, and count how many sprout after the expected days. Six of ten means roughly 60 percent.

Why sow more seeds than plants I want?

No seed lot germinates perfectly, and seedlings are lost to damping-off, pests, and thinning. Sowing only your target count leaves gaps. Dividing by the germination rate and a survival factor compensates so the final stand matches your goal.

What is the thinning or survival factor?

It is the fraction of germinated seedlings that survive to become established plants after thinning, transplant shock, and early losses. A value of 0.9 means you expect to keep nine of every ten that sprout. Lower it for tricky crops or rough conditions.

Does old seed change the math?

Yes. Germination drops as seed ages, so last year's lettuce at 95 percent may only manage 70 percent this year. Run a fresh germination test and enter the lower rate, and the tool automatically tells you to sow more to hit the same stand.

Can I use this for a whole bed instead of per cell?

Absolutely. Enter your total target plant count for the bed and the tool returns total seeds to sow. Use the per-cell mode by entering one or two plants per cell to get a clean per-cell sowing number for plug trays.

Seed Germination Rate & Sowing Density Calculator

Sowing the exact number of seeds you want plants almost always leaves gaps, because germination is never perfect and seedlings are lost along the way. This calculator works backward from the stand you actually want to the number of seeds you must sow to get there.

How it works

Two losses are accounted for: seeds that never germinate, and seedlings that fail to establish. The required seed count is your target divided by both:

seeds to sow = target plants / ( germination rate × survival factor )

For example, to end up with 100 plants at 80 percent germination and a 0.9 survival factor:

100 / (0.80 × 0.90) = 100 / 0.72 ≈ 139 seeds

The tool rounds up, because you cannot sow a fraction of a seed and rounding down would leave you short.

Tips and example

For plug or cell trays, set the target to one or two plants per cell and read the per-cell sowing number directly — many growers sow two or three seeds per cell of low-germination crops, then thin to the strongest. Always test old seed before a big sowing: dropping from 90 percent to 60 percent germination raises the seed you need by half. Keep a survival factor between 0.85 and 0.95 for easy crops, and lower toward 0.7 for delicate or direct-sown crops exposed to weather.