The Yeast Pitch Rate Calculator works out how many yeast cells your batch needs and converts that into practical units — grams of dry yeast, number of liquid packs, or millilitres of slurry. Pitching the right amount is one of the biggest levers on clean fermentation and finished-beer quality.
How it works
The industry pitch-rate guideline is expressed in million cells per millilitre per degree Plato:
cells = rate × volume(mL) × gravity(°P)
The standard rates are:
- Ale: 0.75 million cells / mL / °P
- Lager: 1.5 million cells / mL / °P (lagers ferment cold and need roughly double the density)
Original gravity is converted from specific gravity to degrees Plato with the standard cubic:
°P = −616.868 + 1111.14 × SG − 630.272 × SG² + 135.997 × SG³The total cell count is then divided into your chosen yeast format using these common assumptions: a fresh liquid pack ≈ 100 billion cells, dry yeast ≈ 10 billion cells per gram, and slurry ≈ 1 billion cells per millilitre.
Worked example
A 20 L ale at 1.048 (about 11.9 °P) needs:
0.75 × 20,000 mL × 11.9 °P ≈ 178 billion cells
That is roughly 1.8 fresh liquid packs, 18 g of dry yeast, or 178 mL of slurry. Brew the same wort as a lager and the requirement doubles to about 357 billion cells, which is why lagers usually need a starter or several packs.
Notes
- Pack and slurry counts assume fresh, viable yeast; old yeast contains fewer live cells, so size up or build a starter.
- Dry yeast cell density varies by strain (10–20 billion/g); this tool uses a conservative 10 billion/g.
- For large or high-gravity batches, a yeast starter is usually cheaper than buying many liquid packs.