How much instant yeast equals 1 packet (2¼ tsp) of active dry yeast?

Use ¾ tsp less — about 1¾ tsp of instant yeast. Instant yeast has finer granules and a higher concentration of active cells, so roughly 75% of the active dry amount gives the same leavening power.

How much fresh yeast do I need to replace 1 tsp of active dry yeast?

About 3 g of fresh (cake) yeast per teaspoon of active dry yeast — often described as a 3-to-1 ratio by weight. Fresh yeast is roughly 70% water, so you need three times as much to match the same dry-yeast solids content.

Can I substitute sourdough starter for commercial yeast?

Yes, though the timeline changes dramatically. About 60 g of 100% hydration starter replaces one standard yeast packet (2¼ tsp ADY). Because starter also contains flour and water, reduce your recipe flour by 30 g and water by 30 g for every 60 g of starter added. Expect bulk fermentation to take 3–12 hours depending on starter strength and room temperature.

Do I need to proof instant yeast before adding it to dough?

No. Instant (rapid-rise) yeast can be mixed directly into dry ingredients without pre-dissolving. Active dry yeast benefits from a 5–10 minute proof in warm water (38–43 °C / 100–110 °F) with a pinch of sugar to confirm it is alive before you invest time in a full batch.

Why does the rise time change when I switch yeast types?

Rise time depends on cell count and activity level. Instant yeast contains more live cells per gram and is finer-ground, so gas production starts faster — expect your dough to rise 20–25% faster than with active dry. Fresh yeast is very active but short-lived, performing comparably to active dry when fresh. Sourdough starter relies on a community of wild yeasts and bacteria that work far more slowly, often requiring overnight or longer ferments.

How do I store each type of yeast?

Active dry and instant yeast keep for up to 2 years sealed in a cool, dry cupboard; once opened, refrigerate and use within 4 months. Fresh/cake yeast is highly perishable — refrigerate and use within 2 weeks, or freeze for up to 3 months. Sourdough starter keeps indefinitely in the fridge if fed once a week; discard and refresh before baking.

Yeast Conversion Calculator

Whether you are halfway through a recipe and out of one type of yeast, or you simply prefer to bake with a sourdough culture, knowing the correct substitution ratio is the difference between a well-risen loaf and a brick. This yeast conversion calculator handles all four common forms — active dry yeast (ADY), instant (rapid-rise) yeast, fresh/cake yeast, and 100% hydration sourdough starter — and converts between any of them in either direction.

How it works

The calculator normalises each yeast form to a common reference: the mass of active dry yeast solids it contains. Active dry yeast is about 95% dry matter; instant yeast is equally dry but roughly 25–33% more active per gram because of finer grinding and a more concentrated cell count, so the conversion factor is approximately 0.75 (use 75% as much instant as active dry). Fresh cake yeast is about 70% water, meaning only 30% of its mass is yeast solids — hence the classic 3:1 rule (3 g fresh per 1 g ADY). Sourdough starter at 100% hydration is 50% flour, 50% water, with only about 1–3% live yeast by mass, making it the least concentrated form and requiring the largest volume (roughly 60 g starter to replace a standard 7 g sachet of ADY).

Formula:

amount_out = (amount_in × solidsFraction_in) ÷ solidsFraction_out

This single expression works in every direction without special-case logic.

Worked example

A recipe calls for one standard sachet: 2¼ tsp (7 g) of active dry yeast. You want to use fresh cake yeast from a block you bought at the farmers’ market.

Reference solids from ADY: 7 g × 0.95 = 6.65 g solids
Fresh yeast needed: 6.65 ÷ 0.30 = 22.2 g fresh yeast

The same recipe converted to instant yeast:

Reference solids: 6.65 g (same)
Instant yeast needed: 6.65 ÷ (0.95 ÷ 0.75) = 6.65 ÷ 1.267 = 5.25 g ≈ 1¾ tsp

Sourdough starter recipe adjustment

Sourdough starter is not pure yeast — it carries a significant quantity of flour and water that will alter your dough hydration if you simply swap it in without adjusting the rest of the recipe. For every 60 g of 100% hydration starter you add, subtract 30 g flour and 30 g water from your recipe. The calculator shows this adjustment automatically in the Sourdough tab.

Rise time notes

Yeast type	Relative speed	Typical bulk ferment (24 °C)
Instant / rapid-rise	Fastest	45–75 min
Active dry	Baseline	60–90 min
Fresh / cake	Similar to ADY	60–90 min
Sourdough starter	Much slower	3–12 h (or overnight)

Temperature is the single biggest variable outside yeast type: dough rises roughly twice as fast for every 10 °C increase. Always judge by dough volume (doubled), not the clock.