Yeast Conversion Calculator: Active Dry, Instant, Fresh & Sourdough

The four types of yeast

All baker's yeast is the same organism: Saccharomyces cerevisiae, processed differently. The differences in form affect how you use them, not the flavour of the final bread.

Active dry yeast is dried and granulated with a partially dormant outer shell. It needs to be dissolved in warm water before use (proofing). It's the most common form sold in supermarkets and comes in 7g (¼ oz) packets, a convenient standard unit for home bakers.

Instant yeast (also fast-action, rapid-rise, or bread machine yeast) is finer-grained and fully active without proofing. It can be mixed directly into dry ingredients. It's about 25% more potent by weight than active dry, so you use less.

Fresh yeast (cake yeast, compressed yeast) is wet and unpasteurised: highest leavening power, shortest shelf life. Rarely found in supermarkets. Used extensively by professional bakers because it's cheaper at scale and some argue it produces better flavour.

Sourdough starter is a living culture of wild yeast and bacteria maintained through regular feeding. It leavens more slowly and less predictably than commercial yeast, but that unpredictability is the point. Flavour complexity, not pure leavening efficiency, is why bakers use it.

Conversion ratios explained

The conversion ratios used by this calculator:

Active dry to instant: multiply by 0.75. Instant yeast is roughly 25% more potent by weight, so you use 75% of the active dry amount. This is the most consistent conversion in baking. These two yeasts are interchangeable with only this adjustment.

Active dry to fresh: multiply by 3. Fresh yeast is about one-third as concentrated as active dry because it retains most of its water. Three times the weight delivers the same leavening power. Fresh yeast also dissolves without proofing. Crumble it into warm water or directly into the dough.

Active dry to sourdough starter: 1g active dry equals approximately 120g starter at 100% hydration. Important: when you substitute starter, you're adding flour and water (the starter itself is roughly 50% each). Adjust your recipe water and flour accordingly to keep the total hydration correct. Our yeast-to-sourdough converter handles this automatically.

Yeast to sourdough starter

The sourdough equivalence is the most asked-about conversion and the least reliably answered. Every source gives a different number because starter activity genuinely varies. Culture age, feeding schedule, flour type, and feeding recency all affect it.

The commonly cited range is 100–150g of active 100% hydration starter per 1g of active dry yeast. This calculator uses 120g as the midpoint. If your starter is very active and recently fed, lean towards 100g. If it's older or you keep it in the fridge, lean towards 150g.

This ratio doesn't account for extended fermentation time with sourdough. Commercial yeast works in 1–2 hours. Sourdough typically needs 4–12 hours of bulk fermentation depending on temperature and inoculation rate. You're not just swapping an ingredient. You're changing the timeline of the entire bake.

Instant vs. active dry: what actually differs

Both are Saccharomyces cerevisiae, dried. The manufacturing difference is the granule size and the drying temperature. Instant yeast is dried at lower heat, preserving more active cells, and ground finer so it hydrates without a proofing step.

In practice: instant is more convenient and slightly more reliable. Active dry has a longer shelf life and is more widely available. Both produce identical bread if used correctly. The flavour difference, if any, is imperceptible.

One important caveat: if your active dry yeast is old, proofing matters. Dissolve it in 38–43°C (100–110°F) water for 5–10 minutes before adding to your dough. If it foams, it's active. If it doesn't, it's dead and no amount of kneading will save the bake.

Working with fresh yeast

Fresh yeast has a shelf life of 2–3 weeks refrigerated, sometimes up to 4 weeks if kept very cold and tightly wrapped. Signs it's still good: creamy beige colour, fresh bread smell, crumbles cleanly. Signs it's gone: grey or brown spots, slimy texture, sour smell.

You can freeze fresh yeast for up to 3 months. Crumble it into small pieces before freezing so you can measure what you need without thawing the whole block. Thaw in the fridge overnight before using.

Fresh yeast is hard to find in North American supermarkets but common in European ones. If a recipe from a European cookbook calls for it and you can only find active dry, multiply the fresh yeast quantity by 0.33 (or divide by 3) to get the active dry equivalent. This calculator does that automatically.

Standard packet reference

One standard US packet of active dry or instant yeast is 7g (¼ oz, approximately 2¼ teaspoons). This is calibrated to leaven one standard batch of bread dough using 3–4 cups (360–480g) of flour.

One 7g packet of active dry yeast converts to approximately 5.25g of instant yeast, 21g of fresh yeast, and 840g of active sourdough starter. These are the numbers to keep in your back pocket when a recipe refers to a “packet” and you're using a different format.

Frequently asked questions

How do I convert fresh yeast to active dry yeast?

Divide the fresh yeast weight by 3. One teaspoon of fresh yeast (about 6g) equals roughly 2g of active dry yeast. One standard 7g packet of active dry yeast equals 21g of fresh yeast. Fresh yeast is about 70% water by weight, which is why you need three times as much to get the same leavening effect.

Can I substitute instant yeast for active dry yeast?

Yes, they are interchangeable with one adjustment: use 75% as much instant yeast as the recipe calls for active dry (or 1.25× as much active dry when substituting for instant). Instant yeast is about 25% more potent because it's dried at lower heat and retains more active cells. Unlike active dry, instant yeast doesn't need to be dissolved in water before use; you can mix it directly into dry ingredients.

How much sourdough starter replaces one packet of yeast?

One standard 7g packet of active dry yeast is replaced by approximately 840g of active 100% hydration sourdough starter. In practice, most recipes use 15–20% starter (as a percentage of flour weight), which covers the leavening need over a 4–12 hour bulk fermentation. When substituting starter for commercial yeast, you're also adding flour and water, so adjust your recipe's flour and water down to account for what's inside the starter.

Does the type of yeast affect the flavour of bread?

Active dry and instant yeast produce virtually identical flavour; any difference is imperceptible. Fresh yeast proponents argue it produces a slightly more nuanced flavour, but controlled blind tastings rarely confirm this. Sourdough starter is a different story: it produces lactic and acetic acids during fermentation that add real, measurable tanginess and complexity. The flavour difference between a sourdough loaf and a commercial-yeast loaf is significant and not about the yeast per se: it's about the fermentation byproducts.

How do I know if my yeast is still active?

Proof it: dissolve 1 teaspoon of active dry yeast in ¼ cup (60mL) of warm water (38–43°C / 100–110°F) with a pinch of sugar. After 5–10 minutes, it should foam visibly. No foam means the yeast is dead or near dead. Instant yeast is more stable and can usually be used without proofing, but if you're uncertain, the same test applies. Properly stored yeast (sealed, in the fridge or freezer) lasts well past its printed date.