Yeast Pitching Rate Calculator
Enter your batch size and original gravity, count your packs or vials, and let storage age reduce their viability. The calculator compares cells needed with cells available and sizes the starter that closes the gap.
Results
- Viable cells from your packs
- 79 B
- Packs needed (without starter)
- 3
- Cells available
- 79 B
- Shortfall
- 100 B
- Recommended starter
- 0.71 L
How to use the pitching rate calculator
- Enter batch volume and the original gravity you expect.
- Count the packs, vials or slants you will pitch.
- Read the production date and enter the age in months.
- Choose ale or lager, then add a starter if the shortfall is positive.
The target is a rate of 0.75 million cells per milliliter per degree Plato for ales and 1.5 for lagers, applied to your batch volume and the Plato equivalent of your OG. A liquid pack or vial carries about 100 billion cells, a dry 11.5 g pack about 20 billion and a slant roughly 1 billion; liquid cultures and slants lose about 21 percent per month while dry packs lose only about 1 percent. When viable cells fall short, a stirred 1.036 starter grows about 140 billion cells per liter, capped at 200 billion per pack.
The Plato figure the calculator derives comes from your OG - convert any refractometer reading first with the Brix to SG calculator, and confirm the batch strength with the ABV calculator once fermentation is done.
Frequently asked questions
Why do lagers need twice the pitching rate?
Lager fermentations run cold, and yeast metabolism slows sharply at 10-13 C. Underpitched lagers stress the culture and pick up sulfur and acetaldehyde characters that cold aging cannot fully clean. Doubling the rate keeps the fermentation vigorous despite the temperature.
Does dry yeast really lose viability that fast?
No - the 21 percent figure is calibrated for liquid yeast. Dry yeast is far more robust, so the calculator credits a dry pack with about 20 billion cells that fade only about 1 percent a month, while a slant is counted as a single billion-cell culture. Age still matters: a pack well past its date can arrive below the stated count, and dry packs carry roughly a fifth of the cells of a liquid pack.
What happens if I underpitch anyway?
Underpitching lengthens the lag phase, and stressed yeast multiply first and ferment second, which produces more esters, fusel alcohols and acetaldehyde. Some English styles tolerate it deliberately; lagers and clean ales do not. A starter is cheap insurance compared with a stuck or off batch.