Kombucha's tea-to-sugar-to-starter ratio is simple, but it's easy to get wrong when scaling a recipe up or down for a bigger jar or a bigger batch. This calculator applies the standard per-gallon ratio to your exact batch volume so you always brew with the right proportions.
How the Kombucha Ratio Calculator works
Starter percentage is a recipe volume ratio, not a measurement of acidity or contamination control. Follow a reliable first-ferment process with clean equipment, measured pH, controlled time/temperature and inspection for contamination. This calculator does not calculate pH or verify fermentation safety. Pennsylvania Department of Agriculture guidance identifies pH monitoring through fermentation and a 4.2 endpoint; consult the full process, not only a starter ratio.
Inputs and what they mean
Starter percentage is a recipe volume ratio, not a measurement of acidity or contamination control. Follow a reliable first-ferment process with clean equipment, measured pH, controlled time/temperature and inspection for contamination. This calculator does not calculate pH or verify fermentation safety. Pennsylvania Department of Agriculture guidance identifies pH monitoring through fermentation and a 4.2 endpoint; consult the full process, not only a starter ratio.
Limits and edge cases
This calculator scales the standard first-ferment ratio; it doesn't model flavor additions, temperature, brew time, or a second ferment (bottling with fruit or juice for carbonation), which is a separate process with its own timing and ratios. Very large batches are mostly limited by vessel size and SCOBY size, not by the math — the ratios themselves keep scaling linearly. If you're using a much smaller or larger SCOBY than the batch calls for, fermentation speed (not the ingredient ratio) is what changes.