How much starter should I use to replace yeast?

A common guideline is to use 20-30% of the flour weight in starter. For a recipe with 500g flour, use 100-150g of active starter. More starter means faster fermentation; less means a longer, more flavourful rise.

Why do I need to subtract flour and water from the main dough?

Your sourdough starter is a mixture of flour and water. When you add it to the dough, it contributes both. To keep the overall recipe balanced (same total flour, same total water), you subtract what the starter provides from the amounts in the main dough.

What is starter hydration?

Starter hydration is the ratio of water to flour in your starter, expressed as a percentage. A 100% hydration starter has equal weights of flour and water (e.g. 50g flour + 50g water = 100g starter). A 75% hydration starter has less water (e.g. 57g flour + 43g water = 100g starter).

How long does sourdough take compared to yeast?

Sourdough is much slower. A yeasted bread might rise in 1-2 hours, while sourdough typically needs 4-8 hours at room temperature for bulk fermentation, plus 8-16 hours of cold retard in the fridge for flavour development.

How do I account for the flour and water already in the starter?

A 100% hydration starter is 50% flour and 50% water by weight. So 200g of starter contains 100g flour and 100g water. Subtract these amounts from the flour and water in the original recipe. This calculator does this automatically when you enter your starter amount and hydration.

BakeCalcs

Sourdough Recipe Converter

Convert a yeasted bread recipe to sourdough by adjusting flour and water for starter hydration.

Original Recipe Totals

Total Flour in Recipe

Total Water in Recipe

Sourdough Starter

Starter Weight

Starter Hydration

100% = equal flour and water

How We Calculate This

When converting a yeasted recipe to sourdough, you replace the yeast with sourdough starter. But the starter isn't just a leavening agent — it's a mixture of flour and water that contributes to the total dough formula.

The Calculation

Starter flour = Starter weight ÷ (1 + hydration ÷ 100)
Starter water = Starter weight − Starter flour
Adjusted main flour = Total flour − Starter flour
Adjusted main water = Total water − Starter water

Example

Recipe: 500g flour, 350g water, using 150g starter at 100% hydration
Starter contributes: 75g flour + 75g water
Adjusted: 425g flour + 275g water + 150g starter

Frequently Asked Questions

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Last updated: February 2026

All calculations are based on standard ratios and conversions. Results may vary with specific ingredients, equipment, and conditions.