Why brew with a calculator?
Most kombucha mistakes don't happen during fermentation itself, but at the measuring stage: too little sugar starves the culture, too much starter needlessly sours the base, and a poorly timed F2 stays flat or becomes dangerously over-pressurized. The tools above are built on the proven ratios described in our full F1 guide and our F2 carbonation article — all you need to do is enter your jar size or room temperature.
Important: these estimator tools are built on rules of thumb and typical fermentation curves, not a lab measurement of your specific batch. Always taste, burp, and — if you have one — use a pH meter or hydrometer for the final call.