How this calculator works
All three baking yeasts contain the same organism, Saccharomyces cerevisiae, but in different forms. Active dry yeast is dried with a protective coating of dead cells and must be rehydrated in warm liquid. Instant yeast is dried more gently, has finer granules and can be mixed straight into flour. Fresh compressed yeast is moist and perishable. Because the water content differs, equal weights are not equal in leavening power: instant yeast is about 25 per cent stronger than active dry by weight, and fresh yeast is about one third as strong. The 7 g packet used in many North American recipes is about 2 1/4 level teaspoons.
Formula
active dry equivalent = weight x activity, where activity is 1 for active dry, 1.25 for instant and 0.333 for fresh. weight of a type = active dry equivalent / its activity. teaspoons = weight / grams per teaspoon, using 3.1 g per teaspoon for active dry and instant, and 6.2 g per teaspoon for fresh yeast. packets = active dry equivalent / 7 g.
Worked example
A recipe calls for one 7 g packet of active dry yeast. That is 7 x 1 = 7 g of active dry equivalent. It matches 7 / 1.25 = 5.6 g of instant yeast, or 7 / 0.333 = 21 g of fresh compressed yeast. In spoons, 7 g of active dry is 7 / 3.1 = 2.26 teaspoons, and 5.6 g of instant is 1.81 teaspoons.
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Frequently asked questions
Can I use instant yeast instead of active dry?
Yes. Use about three quarters of the weight, or the calculator's instant figure, and mix it directly with the flour. Instant yeast does not need proofing in water, though it is still worth checking that the liquid is not too hot.
How much fresh yeast replaces a 7 g packet?
About 21 g of fresh compressed yeast. Fresh yeast is often sold in 42 g cakes, so half a cake is close to one packet. Crumble it into the liquid and make sure it dissolves before adding flour.
Why does the packet count use active dry yeast?
The 7 g packet is the standard retail size for active dry and instant yeast in North America. It is a convenient unit for recipes, but the yeast inside behaves according to its type, so use the gram and teaspoon outputs for the type you actually have.
Does the conversion apply to brewer's or nutritional yeast?
No. Brewer's yeast and nutritional yeast are inactive or differently processed and do not leaven bread. They are used for flavour or nutrition and cannot be substituted by weight for baking yeast.