How Sourdough Ingredient Ratios Work
Sourdough formulae centre on baker's percentages—ratios expressed as percentages of flour weight. The foundation uses 100% flour as the baseline, with water typically at 65–75%, active starter at 15–25%, and salt at 1.5–2%, depending on your desired crumb structure and fermentation schedule.
Unlike commercial yeast breads, sourdough's leavening comes from a living culture of wild yeast and lactic acid bacteria. This means the ratio of flour to water in your starter itself matters—a 100% hydration starter (equal weights of flour and water) behaves differently than a stiff 60% starter. Your total dough hydration also incorporates the water already present in the starter, which is why calculating total flour and total water separately prevents over-hydration mistakes.
The calculator accounts for starter hydration by decomposing it into its flour and water components, then summing these into your dough's final composition. This ensures your total hydration percentage—expressed as total water divided by total flour—matches your target.
Sourdough Ingredient Formulas
The following relationships govern sourdough dough composition. Each variable represents the weight in grams (or your chosen unit); water can also be measured by volume in millilitres, since 1 g ≈ 1 mL.
Starter needed = (Percentage Starter ÷ 100) × Flour
Salt needed = (Percentage Starter ÷ 1000) × Flour
Starter Flour = (100 × Starter) ÷ (100 + Starter Hydration)
Starter Water = Starter − Starter Flour
Total Flour = Flour + Starter Flour
Total Water = Water + Starter Water
Total Dough = Total Flour + Total Water + Salt
Total Hydration (%) = (Total Water ÷ Total Flour) × 100
Percentage Starter— Proportion of starter relative to flour, typically 15–25% for medium fermentation speedFlour— Weight of bread flour (or other flour) you're adding to the dough, separate from starter flourWater— Weight of water you're adding directly, separate from water in the starterStarter Hydration— Ratio of water to flour in your starter culture, expressed as a percentage (e.g., 100% means equal weights)Total Hydration (%)— Final percentage of total water relative to total flour; higher values (70%+) produce open crumb, lower values (60%) yield tighter structureSalt needed— Amount of salt by weight, calculated at roughly 2% of flour to enhance flavour and control fermentation rate
Understanding Hydration and Dough Character
Hydration is the single most influential parameter in sourdough baking. A 65% hydration dough is tight and easy to handle, ideal for beginners or when shaping strength matters. A 75% hydration dough produces an open, irregular crumb with visible holes—the hallmark of artisan sourdough. Beyond 80%, dough becomes sticky and demands confident handling; bakers often use high-hydration for wet fermentation or when building strength through stretch-and-folds rather than kneading.
Temperature affects your starter's fermentation speed dramatically. Cold kitchens (16–18 °C) slow wild yeast activity, requiring more starter (up to 30%) and longer bulk fermentation (12–16 hours). Warm kitchens (24–26 °C) speed fermentation, allowing 15–20% starter and shorter timings (4–8 hours). Some bakers adjust their percentage starter rather than extending timings, which changes the final hydration—this calculator lets you explore both scenarios instantly.
The salt calculation at 2% of flour serves dual purposes: it improves flavour and strengthens gluten by slowing fermentation slightly. Reducing salt below 1.5% accelerates bulk fermentation; exceeding 2.5% can over-inhibit yeast activity, leading to dense bread.
Common Sourdough Baking Pitfalls
Avoid these frequent mistakes that throw off your ratios and fermentation timings.
- Forgetting starter hydration in your calculations — Many bakers enter 100% of their starter weight as flour, not realizing half of it is water. If your 200 g starter is 100% hydration, it contains only 100 g flour and 100 g water. The calculator automatically partitions this, but if you miscalculate by hand, your dough becomes over-hydrated and slack.
- Scaling recipes without adjusting percentage starter for temperature — A recipe that calls for 20% starter at 22 °C may over-ferment in a warmer kitchen or under-ferment when it's cold. Use the calculator to explore 15–25% starter ranges; match the percentage to your ambient temperature for predictable rise times.
- Measuring water by volume instead of weight — Converting millilitres to grams is almost 1:1 for water, but flour density varies (140–160 g per cup depending on how it's scooped). Always weigh ingredients on a scale for reproducibility. The calculator assumes grams throughout.
- Ignoring the difference between active and discard starter weights — Some recipes call for active (freshly fed) starter, others use discarded starter at different stages of fermentation. Your starter's peak activity occurs 4–8 hours after feeding, when CO₂ is highest but the culture hasn't yet decline. Using sluggish starter requires higher percentages or longer fermentation.
Working with the Calculator
Enter your flour weight first—this is your baseline. Then input your desired hydration percentage; 67–70% is standard for an open crumb. Specify your starter percentage (15–25% is common) and its hydration level. The tool calculates required water, starter, and salt instantly, plus your total dough weight and final hydration.
If you work backwards from a target dough weight—say, you need exactly 1500 g of dough for your banneton—enter that total weight and adjust flour or water until the dough weight matches. The calculator recalculates all dependent values.
For starter hydration, measure your active starter: if you feed it 50 g flour + 50 g water, it's 100% hydration. If you feed 50 g flour + 37.5 g water, it's 75% hydration. Knowing this is essential because the calculator uses it to determine how much of your starter's weight is actually flour (which counts toward your total flour percentage) versus water.