Every sourdough recipe begins with the same question: How much starter should I use? The answer depends on three things—your flour weight, the starter percentage (baker's %), and the starter hydration. This calculator determines the exact amount of starter needed for any recipe while preserving your intended formula.
Professional bakers express sourdough starter as a percentage of the total flour weight, not as a fixed amount. In baker's percentages, flour is always 100%, and every other ingredient is calculated relative to it. This makes recipes easy to compare, scale, and reproduce, regardless of batch size.
Sourdough starter is a living culture made from flour and water that contains wild yeast and beneficial bacteria. Because it already contains both flour and water, it contributes to the recipe's total flour and total hydration. These contributions must be included when calculating a complete bread formula.
Starter hydration describes the ratio of water to flour in the starter. A 100% hydration starter contains equal weights of flour and water, while stiffer or more liquid starters contain different proportions. Healthy starters are commonly maintained using feeding ratios such as 1:1:1, 1:2:2, or 1:5:5 (starter : flour : water), depending on how frequently they are refreshed.
The calculator uses a simple two-step process to determine exactly how much starter you need and what it contributes to your recipe.
For example, if your recipe uses 500 g flour and 20% starter, you'll need 100 g of starter.
For a 100% hydration starter, 100 g of starter contains 50 g flour and 50 g water. This split is critical for maintaining accurate total hydration in your final dough.
Multiply flour weight by starter percentage to get the total starter needed.
Divide starter weight by (1 + hydration) to find the flour contribution.
Subtract flour in starter from total starter weight to find water contribution.
Starter hydration is the ratio of water to flour in your sourdough starter, expressed as a percentage. It directly affects the consistency of your starter and how it performs in your dough.
A sourdough starter needs regular feeding to stay healthy and active. The feeding ratio describes the proportion of starter : flour : water used when refreshing the culture.
| Feeding Ratio | Starter | Flour | Water | Best For |
|---|---|---|---|---|
| 1:1:1 | 1 part | 1 part | 1 part | Daily feeding, warm kitchen |
| 1:2:2 | 1 part | 2 parts | 2 parts | Every 12–24 hours, standard |
| 1:5:5 | 1 part | 5 parts | 5 parts | Infrequent feeding, cold kitchen |
| 1:10:10 | 1 part | 10 parts | 10 parts | Building large starter for baking |
To maintain a specific amount of starter at a given ratio, divide the total desired starter weight by the sum of the ratio parts, then multiply by each part.
Click any card to load these values into the calculator above.
Most sourdough bread recipes use 10%–25% starter (based on the total flour weight). Around 20% is a common starting point for a 100% hydration starter, but the ideal percentage depends on your fermentation schedule, dough temperature, and desired flavor.
Multiply your total flour weight by the starter percentage (baker's %) and divide by 100.
Formula: Starter Weight = Flour Weight × (Starter % ÷ 100)
For example, if your recipe uses 500 g flour and 20% starter, you'll need 100 g of starter.
The calculation is the same regardless of batch size. Simply apply your chosen starter percentage to the total flour weight. For example, 2,000 g flour with 20% starter requires 400 g starter, while 5,000 g flour requires 1,000 g starter.
Yes. Sourdough starter contains both flour and water, so both must be included when calculating your recipe's total flour and overall hydration. Ignoring the starter's contribution changes the true dough hydration.
A 20% starter percentage is suitable for many sourdough recipes. Lower percentages (10–15%) generally produce slower fermentation, while higher percentages (25–30%) ferment more quickly. The best choice depends on your baking schedule and fermentation conditions.
The most common maintenance ratio is 1:1:1—equal parts starter, flour, and water by weight. Other ratios, such as 1:2:2 or 1:5:5, are used when a longer time between feedings is needed or when building a larger starter.
Decide how much starter you want to maintain, then feed it using your chosen ratio. For example, to maintain 300 g of starter at a 1:1:1 ratio, combine 100 g starter, 100 g flour, and 100 g water. Adjust the amounts proportionally to maintain more or less starter.
Using the correct amount of sourdough starter is essential for predictable fermentation and consistent bread. By expressing starter as a baker's percentage and accounting for its flour and water, you can scale recipes confidently without changing the original formula. Whether you're baking a single loaf or mixing large batches, this calculator helps you determine the right starter amount while keeping your hydration and ingredient ratios accurate.
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