Enter the plants you want, expected germination, and the proportion of germinated seedlings you expect to keep through planting. The calculator divides your target by those two rates, adds your optional margin, and rounds seeds and trays upward. It assumes one seed per cell. These are planning assumptions, not a seed viability test.
Seed & tray quantity planner
Estimate one seed per cell using expected germination and seedling survival. The extra margin is optional; results vary.
These tools calculate from your inputs. Save or print with your browser. Check forecasts, soil conditions and seed-packet instructions before planting.
These calculations use your inputs locally in the browser; they do not infer city frost dates. Read our gardening disclaimer and compare all planting tools.
How to use the seed and tray calculator
- Enter the number of plants you want to end up with.
- Enter the germination rate printed on the packet, for example 80 percent.
- Enter the share of germinated seedlings you expect to keep through planting. Ninety percent is a reasonable planning figure for careful growers.
- Add an optional margin for losses, then read the number of seeds and trays.
Worked example
To end up with 48 plants at 80 percent germination and 90 percent survival, divide 48 by 0.72. That gives about 67 seeds. Adding a 10 percent margin brings it to 74 seeds, so a 72-cell tray is not enough and you would round up to two trays.
Notes on accuracy
- Old seed germinates less well. If a packet is more than a year old, use a lower germination figure.
- The calculator assumes one seed per cell. If you sow two seeds per cell and thin later, the seed count will be higher.
- These are planning numbers, not a viability test. A quick damp paper towel test will show how your seed actually performs.
Pair this with the seed-starting calculator to decide when to sow.