Tool
Seed germination rate calculator
Turn a quick home test into a percentage — and decide whether the seed is still worth sowing.
Your result
70% germination
- Seeds tested
- Seeds sprouted
- What to do
- Fair — sow a little thicker than usual.
What this calculator does
It converts a simple home germination test into a percentage, then tells you how to react: sow as normal, sow thicker, or replace the seed. Germination rate is the single most useful thing you can measure about old or saved seed, because it changes how many seeds you need to sow — see the how many seeds to sow tool for that step.
When to use it
- You have leftover packets past their printed date and want to know if they still work.
- You have saved your own seed and want a real figure rather than a guess.
- You are about to sow something important and cannot afford gaps.
- You are sorting a seed box and deciding what to keep and what to bin.
How to use it
- Run a test. Count about 10 seeds onto damp (not soaking) kitchen paper in a sealed bag or tub.
- Keep it warm and out of direct sun, and check every couple of days.
- Count the sprouts. A seed counts once a root or shoot appears.
- Enter both numbers above. Most results show within 7–14 days; slow crops can take longer.
There is a full method in how to test if old seeds are still good.
Worked example
You test 10 seeds from an old lettuce packet. Seven produce a root within a week. That is 70% — fair. Instead of sowing your usual row, you sow roughly half again as many seeds to end up with the same number of plants, and thin the seedlings later.
Why the number matters
Germination rate is not just a curiosity. A batch at 90% needs almost no allowance for failure; a batch at 50% needs about twice as many seeds to give the same crop. Knowing the rate stops you either wasting seed or leaving gaps in a row.
Limitations
- Small samples are rough. Ten seeds gives a useful signal, not a lab figure. For valuable seed, test 20–25.
- Slow seed misleads. Parsnip, parsley and some hardy perennials take weeks; a short test can look like a failure.
- It measures this batch, not the variety, and storage conditions change the result.
Frequently asked questions
How many seeds should I test?
About 10 is enough for a rough figure; 20–25 is steadier for seed you care about. The percentage is more reliable the more you test.
Can I plant the sprouted test seeds?
Yes — lift them carefully and pot them on. The roots are fragile, but it is a genuine head start.
Why did nothing sprout?
Usually age or poor storage (warm and damp). Give slow crops an extra week before deciding, and check the seed was not treated.
Related guides
Sources and research notes
The test method and reaction thresholds follow common horticultural and seed-saving guidance. This is a home estimate, not a laboratory germination test.