FREE SEED TOOL · OBSERVED TEST DATA
Seed Viability Calculator
Turn a real germination test into a practical estimate of how many seeds in a packet may still germinate and how many seeds you may need to sow for a target number of seedlings.
VIABILITY CALCULATOR
Estimate viable seeds before you sow.
Enter the results of a germination test to estimate how many seeds in a packet may still germinate—and whether the packet can cover your target.
SAMPLE SIZE SIGNALUSEFUL
At this observed germination rate, the packet estimate covers the target with about 20 viable seeds beyond the target.
FORMULA
Observed germination % = germinated ÷ tested × 100 · estimated viable seeds = packet × rate · seeds needed = target ÷ rateEstimate viability from your own germination result.
The calculator first works out the observed germination rate: seeds germinated divided by seeds tested. It then applies that observed rate to the number of seeds remaining in the packet.
If 16 of 20 tested seeds germinate, the observed rate is 80%. If 50 seeds remain in the packet, a simple viability estimate is 50 × 0.80 = 40 seeds. That does not guarantee exactly 40 seedlings; it is a planning estimate based on the test you entered.
Convert an observed rate into a sowing allowance.
When you enter a target seedling count, the calculator divides the target by the observed germination rate. At an 80% observed rate, a target of 20 seedlings gives 20 ÷ 0.80 = 25 seeds.
This compensates only for the observed non-germination rate. It does not include later losses from damping-off, thinning, transplant damage, pests, disease or poor growing conditions.
A larger test usually gives a more useful planning signal.
A very small test can swing sharply because of only one or two seeds. Testing 4 seeds and seeing 3 germinate gives 75%, but one different outcome would change the result by 25 percentage points. A larger sample makes each individual seed less influential.
The sample-size indicator in the calculator is deliberately simple. It does not turn a home germination test into a laboratory certification. Seed lot uniformity, test conditions, temperature, moisture and test duration still matter.
Packet age alone does not tell you how many seeds will germinate.
Seed longevity varies by species and storage conditions. Heat, humidity, seed quality and packaging all influence how quickly performance falls. That is why this calculator asks for an observed germination test rather than applying a generic age-based percentage.
If you have not tested the packet yet, use the Seed Germination Rate Calculator first. It stores the actual batch result locally so you can build evidence from the seed you own.