Guide · reviewed November 14, 2026
Calculate growing mix for seed trays
Measure filled cell volume instead of assuming every tray with the same cell count is identical.
Open Seedling Batch Calculator →Cell count does not define volume
Two 72-cell trays can have different depths, tapers and fill levels. The number of cells alone is not enough to calculate mix. Use the filled volume per cell supplied by the manufacturer or measure a representative cell to the intended fill line. Internal dimensions are the useful dimensions for a geometric estimate.
Use a representative measurement
A practical volume measurement includes the usable fill depth and shape. The optional helper estimates a rectangular or round tapered cell from centimeter dimensions. Real trays may have rounded corners, ribs or drainage details, so a measured capacity can be more reliable. Enter the result in milliliters. One thousand milliliters is one liter.
Round bags after adding reserve
For 72 filled cells of 40 mL each, the nominal volume is 2.88 L. A 10% reserve raises it to 3.168 L. A 10 L bag would cover that modeled batch, but product compaction, moisture and losses can change the usable amount. The final-tray checkbox determines whether empty spare cells are included in the media calculation. Use an appropriate seed-starting medium; the linked extension guidance explains container and mix considerations.