The Science of Baker's Percentages: Calculating Sourdough Hydration and Levain Fractions

In professional baking and artisan sourdough formulation, recipes are never written in static cups or ounces. Instead, bakers rely on Baker's Math—a standardized formula notation where total flour weight is treated as 100%, and all liquid, starter, and salt ingredients are calculated relative to that baseline.

1. Why Baker's Percentages Matter

Standard culinary recipes express ingredients as percentages of the total recipe batch weight. In contrast, Baker's Percentages set Total Flour Weight to exactly 100%.

This mathematical structure enables artisan bakers to scale recipe formulas seamlessly from a single 500g home loaf to a 200kg commercial bakery batch without altering crumb structure, dough elasticity, or fermentation dynamics.

2. The Mathematical Hydration Formula

The hydration percentage determines the open crumb structure, gluten network strength, and dough handling characteristics:

• 65% - 70% Hydration: Stiffer dough, easy to shape, ideal for beginners, round boules, and sandwich loaves.
• 75% - 80% Hydration: Open, airy wild crumb structure typical of high-hydration sourdough and rustic batards.
• 85%+ Hydration: Wet, highly extensible dough suitable for focaccia, ciabatta, and advanced handling techniques.

3. Factoring Starter (Levain) Fractions

A frequent calculation error in home sourdough baking is treating added water and flour as the entire hydration equation while ignoring the liquid and flour contained inside the sourdough starter (levain).

An active sourdough starter fed at a 1:1:1 ratio (100% hydration) consists of 50% flour and 50% water by weight. For exact precision, those fractions must be added to the overall recipe total:

Levain Flour = Levain Weight / 2
Levain Water = Levain Weight / 2

Total Flour = Main Flour Added + Levain Flour
Total Water = Main Water Added + Levain Water

True Hydration % = (Total Water / Total Flour) * 100

4. Step-by-Step 75% Hydration Recipe Breakdown

Consider a formula calling for 500g total flour weight at 75% hydration with 20% levain inoculation and 2% salt:

• Total Flour Baseline (100%): 500 grams
• Levain Inoculation (20%): 100 grams (contains 50g flour + 50g water)
• Salt (2%): 10 grams
• Total Target Water (75%): 375 grams
• Main Flour to Measure: 500g - 50g = 450 grams
• Main Water to Measure: 375g - 50g = 325 grams

5. Multi-Loaf Batch Weight Scaling

To calculate how much flour and water you need for a target total batch weight (e.g. three 800g dough loaves = 2400g total batch weight), sum the total percentage points of all ingredients:

Total Formula % = 100% (Flour) + 75% (Water) + 2% (Salt) = 177%

Total Flour Needed = (Target Batch Weight / Total Formula %)
Total Flour Needed = (2400g / 1.77) = 1355.9 grams