🍞SourdoughCalc
Bidirectional Leavening & Hydration Math

Yeast to Sourdough Converter

Convert any conventional yeasted bread, pizza, brioche, or cinnamon roll recipe to natural sourdough starter—or reverse-convert sourdough formulas to commercial yeast—with zero hydration drift.

SourdoughCalc's Yeast to Sourdough Converter translates commercial yeast (Instant Dry, Active Dry, or Fresh Cake Yeast) into wild levain using the 20% baker's-percentage rule: 1 standard packet of Instant Dry Yeast (7.0g / 2¼ tsp) or Active Dry Yeast (8.75g) converts to 100.0g of active 100%-hydration starter (requiring -50.0g recipe flour and -50.0g recipe liquid).

1 Packet IDY (7g / 2¼ tsp)
100g Active 100% Starter
Mandatory Mass Deduction
-50.0g Flour & -50.0g Water
IDY : ADY : Fresh Ratio
1.0 : 1.25 : 3.0 by Weight
Bulk Time Multiplier
3.5×–4.5× Slower vs Yeast

Boundary Caveat: Commercial Saccharomyces cerevisiae ferments 3.5× to 4.5× faster than wild sourdough microflora; converting a 60-minute yeasted brioche or cinnamon roll with >15% butter/sugar requires boosting levain to 25%–30% or using a stiff sweet levain below.

Bidirectional Leavening Engine100% True Total Hydration Preservation

Commercial Yeast ↔ Sourdough Starter Converter

Original Yeasted Recipe Inputs

Starter Sizing Method:
Target Levain Inoculation (% of Flour)20%
10% (Overnight Slow)20% (Artisan Standard)30% (Fast Sweet Dough)
Your Sourdough Starter Hydration100%

Converted Sourdough Formula

True Hydration: 70%
Add 100g Active Starter (Replaces Commercial Yeast):
Flour Inside Starter50g
Water Inside Starter50g
Final Mixing Bowl Checklist:
Active Sourdough Starter (100%):
100g
Adjusted Main Flour (Deducted 50g):
450g
Adjusted Main Liquid (Deducted 50g):
300g
Bulk Fermentation Shift: Wild yeast rises 3x–4x slower than commercial yeast. Expect 4.0 – 5.5 hours at 76°F (24°C) until dough increases 50%–75% in volume.
SourdoughCalc Bidirectional Leavening Solver • Zero Hydration Drift

The Exact Math of Converting Commercial Yeast to Sourdough

When converting a commercial yeast recipe (such as sandwich bread, focaccia, or enriched brioche) to natural sourdough, simply swapping a 7g packet of dry yeast for 100g of sourdough starter without adjusting the base ingredients will ruin your dough's rheology.

Because active sourdough starter is a hydrated suspension of flour and water, adding starter changes your total flour and water balance. At standard 100% hydration:

Starter Added (20% Rule) = Recipe Flour × 0.20
Deduct Flour = Starter Weight / (1 + Starter Hydration)
Deduct Liquid = Starter Weight − Deducted Flour

To understand how hidden levain water affects gluten extensibility, read our foundational research on The Science of True Total Hydration and Baker's Percentages Demystified.

Commercial Yeast Packet & Teaspoon to Sourdough Starter Conversion Chart

Commercial Yeast MeasureInstant Dry (IDY)Active Dry (ADY)Fresh Cake YeastActive 100% StarterSubtract FlourSubtract Water
1/2 Teaspoon1.5g1.9g4.5g22g-11.0g-11.0g
1 Teaspoon3.1g3.9g9.3g45g-22.5g-22.5g
1.5 Teaspoons (1/2 Tbsp)4.6g5.8g13.8g66g-33.0g-33.0g
1 Standard Packet (2¼ tsp)7.0g8.75g21.0g100g-50.0g-50.0g
2 Standard Packets (4½ tsp)14.0g17.5g42.0g200g-100.0g-100.0g

Master Leavening Equivalency Table (Per 500g Total Flour)

Leavening AgentAmount for 500g FlourFlour & Water AdjustmentTypical Bulk Rise (76°F / 24°C)
Instant Yeast (IDY)7.0g (2¼ tsp / 1 packet)None (0g flour, 0g water)1.0 – 1.5 hours
Active Dry Yeast (ADY)8.8g (~2¾ tsp)None (bloom in warm recipe water)1.5 – 2.0 hours
Fresh Cake Yeast21.0gNone1.0 – 1.5 hours
100% Liquid Sourdough Starter100.0g (20% inoculation)Subtract 50g Flour & 50g Water4.0 – 5.5 hours
50% Stiff Starter (Lievito Madre)100.0g (20% inoculation)Subtract 66.7g Flour & 33.3g Water4.5 – 6.0 hours (low acidity, high loft)
Converting Sweet & Enriched Doughs (Brioche, Cinnamon Rolls)

High sugar (>10% baker's percentage) creates osmotic pressure that slows wild sourdough yeast, while butter and eggs coat gluten strands. When converting enriched commercial yeast recipes to sourdough, increase your starter inoculation to 25%–30% or switch to a 50% hydration stiff starter (Lievito Madre) to prevent sourness from overpowering delicate dairy aromas.

Conversion & Enriched-Dough Masterclasses
How to Convert Commercial Yeast to Sourdough Starter (Zero Hydration Drift)Read Masterclass →Tangzhong & Yudane Enriched Sourdough ScienceRead Masterclass →
Exact Yeast ↔ Sourdough Conversion Reference Guides (Wave 4)
Convert 7g (1 Packet) Instant Yeast to Sourdough (500g Flour)Open Reference Table →Convert 3g (1 tsp) Active Dry Yeast to Sourdough (500g Flour)Open Reference Table →Convert 21g Fresh Cake Yeast to Sourdough (1000g Flour)Open Reference Table →Convert 100g Liquid Starter (100% Hyd) to Commercial YeastOpen Reference Table →Convert 50g Stiff Levain (50% Hyd) to Commercial YeastOpen Reference Table →Convert 200g Sourdough Starter (100% Hyd) to Commercial YeastOpen Reference Table →
Next Step in Your Bake

Need to Build Your Levain or Time Your Bulk Rise?

Once you know how many grams of active starter your converted recipe requires, use our Starter Feeding Calculator to build exact levain with zero waste, or predict your fermentation rise target.

Starter Feeding Calculator →Bulk Fermentation Tool