The reference line is total flour
Add every flour in the formula before calculating percentages. Bread flour, whole wheat flour, rye flour, and flour contributed by a preferment all belong to the total-flour reference when you are comparing complete formulas.
Once total flour is known, divide each ingredient weight by total flour and multiply by 100. A formula with 500 g flour and 375 g water has 75% hydration because 375 ÷ 500 × 100 = 75.
Worked scaling example
For 500 g flour at 75% water, 2% salt, and 20% starter, the direct ingredient weights are 375 g water, 10 g salt, and 100 g starter. The measured total is 985 g when starter is treated as a single ingredient line.
To scale the same ratios to 800 g flour, multiply each percentage by 800 g: 600 g water, 16 g salt, and 160 g starter. The percentages stay unchanged even though every weight is larger.
How to verify a converted formula
Recalculate one line by hand before trusting a copied recipe. Water weight divided by flour weight should return the displayed hydration, and salt weight divided by flour weight should return the displayed salt percentage.
Do not mix the “starter as one ingredient” view with a “starter split into flour and water” view in the same total. Use the sourdough hydration calculator when you need total flour and total water after splitting the starter.
Related calculators
DoughMath guides are educational explanations for formula math. Use the linked calculators for exact weights before baking.