Sourdough Bread Calculator

Understanding Sourdough Baker's Math

The Sourdough Bread Calculator calculates water, starter, and salt quantities for sourdough bread with automatic hydration adjustment for pre-fermented flour.

The Overlooked Detail: Pre-Fermented Flour

Most sourdough recipes list a "flour" amount and a "starter" amount as if the starter were a single ingredient. In reality, sourdough starter is a mixture of flour and water in a known ratio. A 100% hydration starter is 50% flour and 50% water by weight. A 75% hydration starter is about 57% flour and 43% water. When the recipe calls for 100 g of 100% hydration starter, that starter brings 50 g of flour and 50 g of water into the dough — quantities that must be accounted for when calculating the true hydration.

This is the calculation that separates a precise sourdough formula from a rough approximation. Without it, a baker targeting 70% hydration might actually produce a dough closer to 73% or 74%, depending on how much starter the recipe uses. For bread styles where the difference between 70% and 74% changes the crumb structure and handling properties, this matters. The calculator performs this decomposition automatically: enter the base flour weight, target hydration, starter percentage, salt percentage, and starter hydration, and it produces the exact grams of each component to add.

How the Calculator Works

The tool follows a five-step process internally.

1. Calculate starter weight as a percentage of the base flour: if base flour is 500 g and starter percentage is 20%, the starter weight is 100 g.
2. Decompose the starter into flour and water. For a 100% hydration starter: flour from starter = 100 ÷ (1 + 1.00) = 50 g; water from starter = 100 − 50 = 50 g.
3. Sum total flour (base flour + flour from starter) and calculate the total water needed to reach target hydration: total water = total flour × hydration.
4. Subtract the water already contributed by the starter to find how much additional water to add.
5. Calculate salt as a percentage of total flour (not base flour), producing the final recipe.

Step 2 is the critical one. The denominator (1 + starter hydration as a decimal) splits the starter weight into its flour and water components. This formula works for any starter hydration: 60%, 80%, 100%, 125%, or any other value.

Diagnosing Sticky or Dry Dough

When sourdough does not behave as expected, the cause often traces back to a hydration miscalculation or a flour variable. The following troubleshooting flow helps identify the issue.

Symptom: dough is too slack and sticky, hard to shape.

• Check whether pre-fermented flour was accounted for. If the starter water was not subtracted from the total water, the actual hydration is higher than the target.
• Check the flour type. Whole wheat, rye, and spelt absorb water more slowly than white flour. An autolyse (30–60 minute rest of flour and water before adding starter and salt) allows these flours to fully hydrate.
• Check the starter activity. An overly mature (acidic) starter degrades gluten, making the dough feel wetter than its hydration suggests.

The acid produced by lactobacillus bacteria in an over-fermented starter weakens the gluten network, creating a dough that behaves as if it had 5–10% more water. Feeding the starter 4–6 hours before mixing and using it when it has just peaked (doubled in volume and slightly domed on top) produces the strongest dough.

Symptom: dough is too stiff, tears when stretched.

• Hydration may be set too low for the flour type. Whole grain flours need 5–10% more water than white flour for comparable dough feel.
• Salt may have been added early (during autolyse), which tightens gluten prematurely. Add salt after the autolyse period.
• The starter hydration may have been entered incorrectly. A stiff starter (60%) contributes significantly less water per gram than a liquid starter (100%), so the "additional water" value will be higher.

When adjusting hydration, change by 2–3% at a time rather than making large jumps. The difference between 70% and 75% hydration in a bread dough is surprisingly noticeable — the dough goes from a smooth, manageable ball to a sticky, extensible mass that requires different handling techniques.

Starter Hydration and Its Impact

The hydration of the starter itself affects three things: how much additional water the recipe needs, the flavour profile of the bread, and the fermentation speed.

A stiff starter (50–65% hydration) favours acetic acid production, which creates a more sour, tangy flavour. It ferments more slowly and can tolerate longer time between feedings. A liquid starter (100–125% hydration) favours lactic acid, producing a milder, creamier sourness. It ferments faster and needs more frequent feeding.

From a mathematical standpoint, switching from a 100% hydration starter to a 60% hydration starter while keeping all other variables constant will require about 20–30 g more additional water (for a 500 g flour recipe) to maintain the same target hydration. This calculator handles that adjustment, so bakers who maintain different starter consistencies can compare results directly. For understanding how these ratios connect to the broader framework of standard baker's percentage formulas, each value in the sourdough formula maps to a conventional baker's percentage once the pre-fermented flour is accounted for.

Fermentation Timing by Starter Percentage

The amount of starter (as a percentage of base flour) controls how quickly the dough ferments. Lower starter percentages produce a slower rise with more flavour development; higher percentages accelerate fermentation.

These timings assume a room temperature of approximately 25 °C (77 °F). Lower temperatures slow fermentation roughly by half for every 5 °C decrease. A cold retard in the refrigerator (3–5 °C) can extend bulk fermentation to 12–18 hours, which develops flavour without over-proofing. Converting these temperatures between scales is straightforward with an oven temperature converter.

Adapting Recipes Between Sourdough and Commercial Yeast

Converting a commercial yeast recipe to sourdough (or vice versa) is not a simple ingredient swap. Sourdough starter brings flour and water that change the recipe's balance, and it ferments at a different rate than commercial yeast. A rough starting point is to replace the yeast with 20% starter (relative to flour weight) and reduce the recipe's water by the amount the starter contributes. For precise yeast-to-starter ratios, the yeast type conversion tool provides the equivalent amounts. For those just beginning with sourdough, a complete sourdough baking guide covers starter creation, feeding schedules, and first-loaf instructions.

Scaling Sourdough Recipes

Because sourdough formulas are expressed as percentages of flour weight, scaling is straightforward: choose the new flour weight and multiply every ingredient by the same factor. The percentages remain constant. A 500 g flour recipe at 70% hydration that produces a 946 g loaf can be doubled to 1,000 g flour for a 1,892 g batch (two loaves) without changing any ratio. For loaf sizes outside simple multiples, a batch scaling tool handles the arithmetic. When scaling significantly (for example, tripling a recipe), also consider the baking time adjustments that larger or smaller loaves require due to heat penetration differences.

Limitations

This calculator assumes a single flour type for the base flour input. Recipes with multiple flours (for example, 80% bread flour and 20% whole wheat) should use the combined weight as the base flour value. The tool does not separately track the hydration requirements of different flour types, so bakers using high-absorption flours should increase the target hydration manually by 5–10%. Starter hydration must be entered as a known value — if uncertain, the standard assumption is 100% for liquid starters maintained at equal parts flour and water by weight. The calculator also does not account for mix-ins (seeds, nuts, dried fruit) that absorb water; add these after the initial mix and adjust hydration by feel if the dough stiffens.

Key Terms

Pre-Fermented Flour

Flour that has already been mixed with water and fermented as part of a sourdough starter or preferment before being added to the final dough. In baker's math, pre-fermented flour (abbreviated PFF) must be included in the total flour count when calculating hydration.

Autolyse

A rest period (typically 30–60 minutes) during which flour and water are mixed and left to hydrate before the starter and salt are added. Autolyse allows flour to absorb water fully, begins gluten development, and makes the dough easier to work with. It is particularly beneficial for whole grain flours that absorb water slowly.

Bulk Fermentation

The first rise of the dough after all ingredients are mixed. During bulk fermentation, yeast produces carbon dioxide (causing the dough to expand) and organic acids (developing flavour). The duration depends on starter percentage, temperature, and desired sourness. Also called the first proof or primary fermentation.

Cold Retard

A technique in which shaped dough is placed in the refrigerator (3–5 °C / 38–41 °F) for 12–18 hours. The cold temperature slows yeast activity, extending fermentation and deepening flavour without over-proofing the dough. Most sourdough recipes benefit from a cold retard for improved flavour complexity and baking convenience.