Germination Rate Calculator: Percentage and Seeds
Germination rate is the share of seeds that sprout. Test a batch to get your rate, then use it to decide how many seeds to sow for 12 tomato plants or 100 plants in a row, or to predict how many plants a sowing will give. Results are estimates, because a rate from a small test varies from one sowing to the next.
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Formula
- Germination rate (%) =
sprouted / sown x 100 - Seeds to sow =
plants wanted / (rate / 100), rounded up to a whole seed - Expected plants =
seeds sown x rate / 100
The rate comes from a test, so the predicted number of plants is an estimate. Real sowings also lose seedlings to weather, pests and disease.
Worked example
- 18 of 25 seeds sprout: 18 / 25 x 100 = 72%.
- 40 plants wanted at 85%: 40 / 0.85 = 47.06, so sow 48 seeds.
- 100 seeds at 85% give about 85 plants.
- 12 plants wanted at 80%: 12 / 0.80 = 15 seeds.
When to use it
Use the rate mode after a paper towel test of older seed to see if it is still worth sowing. Use the seeds mode when you need an exact number of plants, for example filling a row or a set of pots. Use the expected mode to plan how many seedlings to make room for. The percentage printed on a packet is a typical value for fresh seed; stored seed usually does worse.
A note on test size
Each seed in a 10-seed test is worth 10 percentage points, and in a 25-seed test it is worth 4. A larger test gives a steadier answer, so test 20 or more seeds if the result matters.
Common mistakes
- Dividing by the wrong number: use the seeds sown, not the seeds that failed.
- Rounding down when working out seeds to sow. Always round up.
- Mixing germination with emergence in the field. Field emergence is usually lower than a warm indoor test.
How it differs from nearby calculators
This page works on percentages of seeds. The seed quantity calculator turns a planting area and spacing into the seed you need, and the plant spacing calculator counts plants per bed. Use the planting date calculator to choose when to sow.
Frequently asked questions
How do I calculate germination rate?
Divide the number of seeds that sprouted by the number you sowed and multiply by 100. If 18 of 25 seeds sprout, the rate is 18 / 25 x 100 = 72%.
How many seeds should I sow to get a set number of plants?
Divide the plants you want by the germination rate (as a decimal) and round up. For 40 plants at 85%, 40 / 0.85 = 47.06, so sow 48 seeds. Many gardeners sow a few extra to allow for losses after sprouting.
How do I test seed germination at home?
Place 10 or more seeds on a damp paper towel, seal it in a bag and keep it warm. Count the sprouts after the number of days given for the crop. Testing 20 seeds gives each seed a weight of 5%, so a larger test gives a steadier answer.
What is a good germination rate?
It depends on the crop, the seed age and the storage. Fresh vegetable seed is often 80% or more, but some herbs and flowers are lower. The percentage printed on a packet is a typical value for fresh seed, so test older seed before relying on it.
How many seeds do I sow for 12 plants at 80 percent germination?
Divide the plants you want by the rate as a decimal: 12 / 0.80 = 15 seeds. Because 15 is a whole number no rounding is needed, but many gardeners still sow one or two extra for losses after sprouting.
How many seeds for 100 plants at 90 percent germination?
100 / 0.90 = 111.1, which rounds up to 112 seeds. Always round up, since 111 seeds would give only about 99.9 plants on average.
How many seedlings will I get from 200 seeds at 75 percent?
Multiply the seeds by the rate: 200 x 0.75 = 150 expected seedlings. This is an average; an actual sowing can land a few above or below, and field conditions can cost more plants later.