Tool
How many seeds to sow
Turn a germination rate into a sowing quantity, so you end up with the plants you want.
Your result
Sow about 18 seeds
- Plants wanted
- Germination rate (%)
What this calculator does
If only 70% of a packet will sprout, sowing 12 seeds to get 12 plants leaves you short. This tool divides the number of plants you want by the germination rate, so a low rate automatically means sowing more. It is the natural second step after testing a batch — see the germination rate calculator.
When to use it
- Using older seed whose germination you have tested.
- Working with precious or limited seed, where you cannot afford to waste any.
- Planning a bed where you need an exact number of plants.
How to use it
- Decide the plants you want. For a bed, use the spacing calculator to get this number.
- Enter your germination rate. If you have not tested the batch, use a sensible estimate — or test it first.
- Sow the result and label the packet with the rate for next time.
Worked example
You want 12 plants and the batch tests at 70%. 12 ÷ 0.7 = 17.1, so you sow 18 seeds. If the same batch tested at 95%, 12 ÷ 0.95 = 12.6, so 13 seeds would do. The weaker the seed, the more you must sow to get the same crop.
Don't forget losses after germination
Germination is not the only thing that thins a crop. Seedlings are lost to damping off, damage when pricking out, slugs and dry spells. For anything you really need, add a small buffer on top of the calculated figure — a few extra seeds, or one or two spare plants — rather than relying on a perfect result.
Limitations
- It assumes even germination. A real tray never sprouts perfectly uniformly.
- It ignores seedling losses after sprouting, so treat it as a minimum.
- It cannot invent vigour. Very old seed may germinate but grow weakly; fresh seed is still the better choice for a main crop.
Frequently asked questions
What germination rate should I assume?
If you have not tested, assume a high figure for fresh seed and a cautious one for old seed — or run a test and use the real number.
Should I always add extra seeds?
For a main crop, yes — a small buffer covers transplant losses. For scarce seed, sow exactly and handle the seedlings gently.
Does this work for direct sowing outside?
Yes, but outdoor germination is usually lower than a warm indoor test, so treat the calculated number as a minimum.
Related guides
Sources and research notes
This is a straightforward planning calculation based on the germination rate you enter; it does not predict your actual results.