United StatesTier 2
Yeast starter calculator
Batch volume, OG and yeast pack in. Target cell count, cells on hand, and starter size to close the gap out.
Free·No sign-up·Last checked 2026-08-27
Formula
°Plato ≈ (OG − 1) × 1000 ÷ 4
Target cells (billion) = pitch rate × volume_mL × °Plato ÷ 1000
Cells on hand = packs × cells/pack × viability%
Starter volume (L) ≈ cell deficit ÷ 130 (stir-plate growth at ~1.040)
DME = 100 g per liter of starter
Worked example. 5 gal at 1.060 needs 213B cells; one 90%-viable liquid pack provides 90B, a deficit of 123B, needing about a 0.95 L starter.
Method
Simplified stir-plate growth model
This is a practical approximation, not a full log-growth curve — it assumes a roughly 130 billion cell yield per liter of 1.040 stir-plate starter, a commonly cited round number. Actual growth varies with strain, oxygenation and stir speed, so round the result up to a convenient flask size.
Questions
A dry packet ships with far more viable cells than a liquid vial or smack pack, so it often already meets the target pitch rate for ordinary-gravity beers without any additional growth.
No — it's a simplified stir-plate growth estimate, not a full log-growth model. Real growth depends on wort gravity, oxygenation, stir speed and yeast strain. Treat the result as a starting point and round up to a convenient size.
A shaken starter without agitation still grows cells, just less efficiently than a stir plate. Sizing up the starter somewhat compensates, though this calculator assumes stir-plate efficiency.