Seed starting
Seed tray, seed & growing mix calculator
Enter the plants you want and the tray you use. The result shows seeds, cells, mix and a tray allocation.
Plants to grow
Use your seed test or packet rate. Usable seedlings is the share of germinated cells expected to reach transplant quality.
Trays & growing mix
Estimate cell volume from dimensions
Internal measurements in centimeters; depth ends at your fill line. A measured fill volume is more reliable than geometry.
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Seedling batch
Editable assumptionsTray allocation
Cells are allocated in crop order. The diagram is a counting aid, not a model of your tray’s actual row layout.
Expected plants are an estimate, not a guaranteed yield. Multiple seeds per cell are modeled as independent germination events; real seed lots and growing conditions can be correlated.
Guides
How many seeds should you sow for a transplant target?
Distinguish germination, usable seedlings, multiple seeds per cell and rounding.
Calculate growing mix for seed trays
Measure filled cell volume instead of assuming every tray with the same cell count is identical.
Allocate mixed crop batches across trays
Count the required cells, label crops and keep the last tray’s spare capacity visible.
How the tool works
For n seeds per cell and germination probability g, the model estimates at least one germination as 1 − (1 − g)ⁿ. It multiplies that by your usable-seedling fraction, then divides the target plants by that probability and rounds up to whole cells. Trays are rounded separately. Media uses the number of filled cells × filled cell volume, plus your reserve. These are expectations under assumptions, not guaranteed yields.
References
Guidance reviewed November 14, 2026. Enter your own measurements and check a test before committing materials. About this tool