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The Sourdough Companion's Formula Lab handles hydration, levain and salt to the gram, and it saves every formula so you can scale it, tweak it and bake it again.
Try the Formula Lab for freeWhat is hydration in bread?
Sourdough hydration is simply the weight of water in your dough expressed as a percentage of the flour, which is the core idea behind baker's percentage. If you mix 500 g of flour with 375 g of water, that is 75% bread hydration, because 375 ÷ 500 × 100 = 75. The flour is always the 100% that everything else is measured against, which is why a hydration figure scales cleanly from one loaf to a dozen.
How to read it
Higher hydration means a wetter, stickier, harder-to-handle dough that tends to bake up with a more open, airy crumb; lower hydration gives a stiffer dough that is easier to shape and holds a tighter structure. This hydration calculator works in both directions so you can either set a target percentage and get the exact water to add, or weigh what you actually used and read back the percentage.
What different levels mean
As a rough guide: around 65% is a firm, beginner-friendly dough with a tighter crumb and predictable shaping; about 75% is the classic everyday sourdough sweet spot, soft and workable with a nicely open crumb; and 85% and up is a slack, high-hydration dough chasing a wild, airy interior that rewards practice and a confident hand. Your flour matters too: strong, freshly milled or whole-grain flours drink more water, so the same percentage can feel quite different from one bag to the next.
How this works (the math): hydration % = water ÷ flour × 100, so water = flour × hydration ÷ 100. Total dough = flour + water (plus any starter you enter). When you add a starter, its flour and water are folded in: starter flour = starter ÷ (1 + starter hydration), starter water = the remainder, then true total hydration = (added water + starter water) ÷ (added flour + starter flour) × 100. Grams round to the nearest whole gram and percentages to one decimal. No false precision.
These are the same conventions used inside The Sourdough Companion app's Formula Lab: a 100%-hydration starter splits half flour, half water, and the true-hydration total includes the levain's own flour and water.
New to the terms? Browse the Sourdough Glossary → — 100+ science-backed definitions, from hydration and true hydration to crumb.