Yeast Pitch Rate Calculator
Yeast pitch rate is the number of viable yeast cells per milliliter of wort per degree Plato needed to start a clean, complete fermentation. The standard targets are 0.75 million cells/mL/°P for ales and 1.5 million cells/mL/°P for lagers. The formula is cells = pitch rate × volume in mL × degrees Plato.
Underpitching is the most common cause of off-flavors in homebrewed beer, and the fix is arithmetic, not equipment.
How pitch rate works
The standard pitch rate for ales is 0.75 million cells per milliliter per degree Plato. A 19 liter batch of 1.055 wort (roughly 13.6 °P) needs about 194 billion cells — two fresh liquid packs, or 19 g of dry yeast.
Lagers double the target to 1.5 million cells/mL/°P, because fermentation at lower temperatures is slower and more demanding on the yeast. A lager at the same gravity needs roughly 388 billion cells.
cells = pitch rate × volume (mL) × degrees Plato
Liquid yeast vs dry yeast
A fresh pack of liquid yeast (White Labs, Wyeast) ships with roughly 100 billion cells. That is enough for a moderate ale but not for a lager, which is why starters exist.
Dry yeast ships at roughly 10 billion cells per gram and stays viable far longer than liquid. An 11.5 g sachet is about 115 billion cells. For most ales, one sachet is close to the right number.
Viability and starters
Liquid yeast loses roughly 20% of its viability per month under refrigeration. A pack bought two months ago has about 60 billion viable cells, not 100. A yeast starter grown on a stir plate can multiply the cell count by a factor of four or more, making a single pack sufficient for a lager.
The Yeast textbook by White and Zainasheff is the standard reference for pitch rate targets and starter sizing.
What underpitching does
Underpitching does not stop fermentation — it makes it slow and stressed, producing more esters, fusel alcohols and diacetyl than a properly pitched fermentation would. These are off-flavors in a clean beer. In a Belgian or wheat beer, where ester production is the point, a modest underpitch can be deliberate.
Yeast Pitch Rate Calculator — questions
How many yeast cells are in a pack of liquid yeast?
A fresh pack of White Labs or Wyeast contains roughly 100 billion cells at the date of manufacture. Viability drops about 20% per month at refrigerator temperature, so a two-month-old pack has roughly 60 billion.
Do I need a starter for a lager?
Almost always, yes. A lager at 1.050 needs roughly twice as many cells as an ale at the same gravity. One liquid pack is rarely enough, so a 1.5–2 liter starter on a stir plate is standard.
Can I overpitch?
In practical homebrewing terms, no. Deliberately pitching more yeast than the textbook rate rarely causes problems and often improves consistency. The risk is underpitching, not overpitching.
Pitch rate calculated from the recipe
Brewgravity reads the OG and batch volume from your recipe and tells you how many packs or grams to pitch — no re-entering numbers on brew day.
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