Yeast Starter Calculator

How it is calculated

The tool works out how many live yeast cells the batch needs. cells (billion) = rate × volume × °P, where rate is the pitch rate in million cells per mL per degree Plato, volume is the batch in litres and °P is the wort gravity in degrees Plato. The unit work behind it: rate × 1000 mL per litre × volume × °P gives million cells, and dividing by 1000 gives billions. A commonly used rate is 0.75 for ales and 1.5 for lagers, but there is no default: you must type the rate yourself. The answer is the required count of viable cells only. It does not say how big a starter to make, how much malt extract to use, or how many cells a vial or packet holds, so you compare it with your own yeast source. Any value of zero or below, or a missing field, returns no result.

Common mistakes

• Entering specific gravity, such as 1.048, in the Plato field. The field is degrees Plato, so convert the reading first; 1.048 typed as °P gives only 15.72 billion cells for the 20 L batch, far below the real need.
• Entering the volume in gallons. The field is litres, so a 5-gallon batch is about 19 L, not 5 (5 gives 45.00 billion cells at 12 °P).
• Using the ale rate for a lager. The lager rate is roughly double, so the cell count you need doubles as well.
• Typing the pitch rate as a total in millions or billions of cells instead of per mL per °P. A value such as 750 is accepted and gives 180,000.00 billion cells.
• Counting the cells on the pack label as if all were alive. The result is viable cells, and old or warm-stored yeast has fewer than the label says, so allow for that.