Yeast Pitch Rate Calculator

This calculator estimates how many yeast cells your batch needs for a healthy fermentation, using the classic homebrewing pitch-rate guideline of cells per milliliter per degree Plato. It first converts your original gravity in points to an approximate Plato reading (points divided by 4), then converts batch volume from gallons to milliliters. Depending on whether you select ale or lager, it applies the corresponding rate — roughly 0.75 million cells/mL/°P for ales and double that, 1.5 million, for lagers, reflecting lagers' cooler, slower fermentations that benefit from a larger cell population. Multiplying rate times volume times Plato and dividing by 1,000 converts the running total from millions to billions of cells.

That raw target is then divided by your entered viability percentage, since dead cells don't ferment: an older pack rated at only 70% viable needs proportionally more total cells added to hit the same living-cell target. The result is expressed as billion cells needed, and divided again by an assumed 100 billion cells per fresh liquid yeast pack to tell you how many packs to buy. If more than one pack is required, the tool recommends a simple 1-liter starter as a rule-of-thumb boost, though real starter sizing depends on more variables (stir plate use, gravity of the starter wort) than this simplified model captures. Keep in mind the whole calculation rests on an approximate points-to-Plato conversion and a single flat viability-decay assumption — it's a solid starting estimate, not a substitute for a full viability calculator based on the yeast's actual production date.