Hydration is the single number that tells you the most about how a sourdough dough will behave — how sticky it feels, how it holds its shape, and what kind of crumb it bakes into. This calculator turns your recipe's flour, water, and starter weights into a precise baker's-percentage hydration, and lets you work backward from a target hydration to the exact weights you need.
Why starter math is different
A starter isn't purely leavening — it's also flour and water that count toward your dough's total hydration. Ignoring it is the most common mistake in hydration math: a 100 g starter fed at 100% hydration is 50 g flour and 50 g water, and both need to be added to your recipe's totals before you divide. A stiffer starter (lower hydration) contributes proportionally more flour than water, which nudges your final hydration down slightly compared to the same weight of a wetter starter.
Reading the hydration bands
Below about 65% hydration, dough is firm and easy to shape by hand — think bagels or a basic sandwich loaf. From 65% to 80% is the sweet spot most home sourdough bakers aim for: manageable dough that still bakes into an open, chewy crumb. Above 80%, dough becomes noticeably sticky and slack, rewarding stretch-and-fold technique over kneading, and producing the big irregular holes associated with ciabatta and rustic artisan loaves.
Scaling a recipe without losing ratios
Baker's percentage exists so you can resize a recipe without recalculating every ratio by hand. The Scale to Target tab lets you fix a target hydration and either a target flour weight or a target total dough weight, then solves for exactly how much flour and water to add — automatically accounting for whatever your starter already contributes. This is the same math professional bakers use to move a recipe from a home batch to a larger one without guessing.