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The Sourdough Companion's Formula Lab handles hydration, levain and salt to the gram — and saves every formula so you can scale it, tweak it and bake it again.
Try the Formula Lab — freeWhat is hydration in bread?
Sourdough hydration is simply the weight of water in your dough expressed as a percentage of the flour — 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.