Yeast Conversion Calculator

Mastering Yeast Type Conversions

The Yeast Conversion Calculator converts between active dry, instant, fresh yeast, and sourdough starter with precise ratios and preparation guidance for each type.

How Yeast Types Differ

All commercial baking yeast belongs to the species Saccharomyces cerevisiae, but the three forms — active dry, instant, and fresh — are processed differently, resulting in distinct handling requirements and potency levels. Sourdough starter uses wild yeast strains alongside lactobacillus bacteria and behaves differently from all three commercial forms.

Active dry yeast (ADY) was the first widely available dry yeast for home bakers, introduced in the 1940s. The granules are coated with dead yeast cells that must be dissolved in warm water (35–40 °C / 95–105 °F) before the live cells inside can activate. Skipping this proofing step with active dry yeast results in clumps of undissolved granules in the dough.

Instant dry yeast (IDY), developed in the 1970s, uses a gentler drying process that keeps more cells viable. The smaller, more porous granules absorb moisture quickly from the dough itself, eliminating the need for pre-dissolving. Gram for gram, instant yeast is about 25% more potent than active dry, which is why the conversion ratio is 0.75× — you need less instant yeast to achieve the same rise.

Fresh yeast (also called cake yeast or compressed yeast) has the highest moisture content and the shortest shelf life. It is the traditional form used in European bakeries and remains popular in countries where it is sold in refrigerated supermarket sections. Because of its water content, three grams of fresh yeast provide roughly the same leavening power as one gram of active dry yeast.

How the Converter Works

Enter the yeast type and amount in grams. The tool first converts the input to an active dry yeast equivalent using a normalisation factor, then calculates the equivalent amounts for all four types.

The conversion ratios, with active dry as the base, are as follows.

• Active dry → Instant: multiply by 0.75
• Active dry → Fresh: multiply by 3.0
• Active dry → Sourdough starter (100% hydration): multiply by approximately 21.43

These ratios are consistent across the range of amounts used in home baking (1–50 g). They are derived from the relative cell viability and moisture content of each yeast form, as documented by yeast manufacturers and corroborated by baking science texts including Tartine Bread (Robertson, 2010) and King Arthur Baking's professional resources.

The Sourdough Starter Equivalence

The sourdough conversion is approximate by nature. A 100% hydration sourdough starter contains roughly equal parts flour and water, with the yeast content varying based on the starter's maturity, feeding schedule, and ambient temperature. The ratio of 21.43× means that 7 g of active dry yeast is approximately equivalent to 150 g of active, recently fed starter.

Because the starter introduces both flour and water into the recipe, a straight substitution changes the dough's hydration. Any recipe converted from commercial yeast to sourdough must account for the flour and water in the starter by reducing the recipe's base flour and water accordingly. The sourdough bread calculator performs this pre-fermented flour decomposition automatically. For those beginning the transition from commercial yeast, a complete sourdough guide covers starter creation and maintenance.

Practical Guidance by Yeast Type

Switching from active dry to instant: Use 75% of the active dry amount and skip the water-proofing step. Add the instant yeast directly to the flour before mixing. The rise time stays approximately the same because the leavening power is equivalent.

Switching from instant to active dry: Use 133% of the instant amount (divide by 0.75) and dissolve in a small portion of the recipe's warm water for 5–10 minutes before adding to the flour. Subtract the proofing water from the total water in the recipe.

Switching from fresh to dry yeast: Divide the fresh yeast amount by 3 to get the active dry equivalent, or by 4 to get the instant equivalent (3 × 0.75 = 2.25, but 4 is the commonly rounded figure for fresh-to-instant). Fresh yeast should be crumbled into the flour or dissolved in lukewarm water.

When adjusting yeast amounts in the context of baker's percentage formulas, express the yeast as a percentage of flour weight for the converted type. A recipe at 1% active dry yeast becomes 0.75% instant yeast — the percentage system keeps the conversion transparent across any batch size. For pizza dough, where yeast quantities are often very small (0.1–0.5%), the pizza dough calculator handles yeast type selection directly within the formula.

Storage and Shelf Life

Active dry and instant yeast in sealed packets last 1–2 years at room temperature. Once opened, transfer to an airtight container and refrigerate — opened yeast loses potency over weeks as it absorbs moisture from the air. Fresh yeast must be refrigerated and used within 1–2 weeks of purchase; it can also be frozen for up to 3 months, though some potency is lost upon thawing.

To test whether yeast is still active, dissolve a teaspoon in warm water with a pinch of sugar. If it foams within 10 minutes, the yeast is viable. If no foam appears, the yeast is dead and should be replaced. Expired yeast does not produce harmful results — it simply fails to leaven the dough.

Limitations

The sourdough starter conversion is an approximation based on a 100% hydration starter at peak activity. Starters maintained at different hydrations (60%, 80%, 125%) will have different ratios of flour and water per gram, and their yeast concentration varies with feeding schedule, temperature, and flour type. The 21.43× ratio should be treated as a starting point; experienced sourdough bakers adjust based on their specific starter's vigour. Additionally, the calculator does not account for fermentation time differences — commercial yeast produces a full rise in 1–2 hours, while sourdough starter typically requires 6–12 hours. To scale yeast amounts alongside a full recipe, the recipe scaling tool applies the same multiplier to every ingredient including yeast.

Key Terms

Active Dry Yeast

A granulated form of Saccharomyces cerevisiae with approximately 8% moisture content. The outer layer of dead yeast cells requires rehydration in warm water (35–40 °C) before the live interior cells can activate. One standard US packet contains 7 g (approximately 2¼ teaspoons).

Instant Dry Yeast

A more finely ground form of dry yeast with approximately 5% moisture content. The smaller granules hydrate rapidly upon contact with flour and water, eliminating the need for pre-dissolving. Also marketed as rapid-rise, quick-rise, or bread machine yeast, though all are functionally equivalent.

Proofing (Yeast)

The process of dissolving active dry yeast in warm water (with a small amount of sugar) to verify that it is alive and active before adding it to the dough. The term "proofing" in this context is distinct from "proofing" a shaped loaf (which refers to the final rise before baking). Instant and fresh yeast do not require a proofing step.