Total hydration is total water weight divided by total flour weight, multiplied by 100. Include the flour and water in your starter. A 100% hydration starter contains equal flour and water weights; it is not 100% water.
Work through one example
Suppose you mix 450 g flour, 290 g water, and 100 g starter at 100% hydration. The starter contributes 50 g flour and 50 g water. Total flour is 500 g; total water is 340 g. Hydration is 340 ÷ 500 × 100 = 68%.
Salt does not enter that calculation. This example demonstrates arithmetic, not a tested bread recipe or a recommended hydration for every flour.
Calculate your own formula
This calculator handles flour, water, and a starter with a known flour-to-water ratio. It does not estimate the water in eggs, butter, fruit, milk, or other additions. For enriched dough, use the recipe’s stated method of accounting.
When the starter is not at 100% hydration
Let starter weight be S and starter hydration as a decimal be H. Starter flour = S ÷ (1 + H). Starter water = S − starter flour. Add those amounts to the final-mix flour and water before calculating the total percentage.
For a second arithmetic check, 90 g starter at 50% hydration contributes 60 g flour and 30 g water. If its hydration is unknown, do not assume the calculation is precise.
What the percentage does not tell you
Hydration alone does not describe dough strength, proofing status, flavor, or food safety. Flour type and the rest of the process still matter. King Arthur’s hydration explainer distinguishes the numerical ratio from how different doughs feel.
Use the result to compare accurately recorded formulas, not to chase a larger number. If the real problem is handling, continue to the sticky-dough guide.
Sources & scope
Source-based explanation and editorial checklists by SourdoughStart, operated by Tag Ad Limited. AI-assisted article revised 2026-10-12. Source links are not endorsements.
Revision note: prepared for the new reference-led edition. Suggest a correction.