Fresh to Dry Yeast Converter

The recipe calls for 30 g of fresh yeast and all you have is a sachet of dry. The swap is not one to one: fresh yeast is mostly water, dry yeast is the same organism dehydrated, so one gram of dry does the work of nearly three grams of fresh. Enter the amount, pick the direction, and you get the grams to use. Thirty grams of fresh comes out around 9.9 g of dry.

The factor built in is 0.33 both ways: fresh times 0.33 gives dry, dry divided by 0.33 goes back to fresh. That ratio matches instant yeast, the kind you stir straight into the flour. If your packet is active dry, the type that has to bloom in warm water first, use roughly 20% more than the tool says, since it carries fewer live cells per gram and some are lost on rehydration.

This is for baker's yeast only. Baking powder, baking soda and sourdough starter follow completely different rules and do not belong in this ratio. In practice, a 42 g fresh cube lands near 14 g of dry, and a 10 g sachet of dry stands in for about 30 g of fresh. Yeast quantity is not fixed law either: less yeast plus a long cold ferment usually tastes better than following the recipe to the gram.