Pitching the right amount of yeast is one of the biggest levers you have over fermentation. Underpitch and the yeast gets stressed, throwing fusel alcohols and risking stalling; overpitch and you lose yeast character. This tool covers both ways most brewers pitch: fresh dry yeast and liquid packs. It works out how many viable cells your beer needs, then tells you what to pitch, and if you are short on liquid yeast it sizes a starter for you. If you are brewing beers with prominent yeast character like a wheat beer or Belgian Ale we would underpitch by 20%.
The simplest path. Tells you the grams and number of sachets to pitch straight in. Dry yeast is dense and stable, so no starter needed.
Ages your packs from the production date, tells you how many fresh packs to pitch, or sizes a starter to grow the packs you already have up to target.
Needs about 214 billion cells: roughly 11 g of dry yeast (one sachet), or just over one 200 billion liquid pack.
Lagers want roughly double, about 339 billion cells, so around 17 g of dry (two sachets), or two liquid packs, or a starter off a single pack.
Specific gravity converts to degrees Plato with the standard cubic:
Then the cell target every calculator agrees on:
And the conversion into what you buy:
If you are short, the starter maths uses Kai Troester's published growth model in billions of new cells per gram of extract:
Troester published his data and method, reproduced by other calculators, at about ±15%. The finding that more cells ferment faster with less net growth is well supported in peer-reviewed work (Verbelen et al., 2008, 2009).
The 0.75 and 1.5 constants come from White & Zainasheff, via George Fix. A sensible default written for re-used yeast, but the literature treats pitch rate as a range, not a setpoint.
The old 21%/month rule comes from a single supplier statement and is harsh for modern packaging. White Labs PurePitch data shows over 80% at four months. We default to that modern curve and let you type in a measured value, which beats any model.
Pitch rate clearly drives fermentation speed, but its effect on esters is genuinely contested in the literature, with oxygenation and scale doing much of the work. Hit a sensible target, stay consistent batch to batch, and control temperature and oxygen before chasing exact cell counts.
