Sourdough Hydration Explained: Baker's Percentages Made Simple

The math behind the dough · Updated July 2026

Every sourdough recipe you'll ever read speaks the same language: percentages. "78% hydration, 2% salt, 20% levain." Once you can read it, you can scale any recipe, compare formulas at a glance, and fix a sticky dough instead of fearing it. Here's the whole system in five minutes.

What hydration means

Hydration is the weight of water relative to the weight of flour. In baker's percentages, flour is always 100% and everything else is measured against it:

• 1000 g flour + 750 g water = 75% hydration
• 500 g flour + 400 g water = 80% hydration

The formula is simply water ÷ flour × 100. Two details trip people up: it's always weight, never volume — and a precise version also counts the flour and water inside your starter. A recipe with 900 g flour, 650 g water and 200 g of 100%-hydration starter really contains 1000 g flour and 750 g water: 75%, not 72%.

Choosing a hydration level

• 65–70%: easier to handle, forgiving during shaping, tighter crumb. The right starting point for your first loaves.
• 75–80%: classic sourdough territory — open crumb potential with manageable stickiness once your hands know what developed dough feels like.
• 80–85%+: wet, sticky and unforgiving, but capable of the big glossy holes you see online. For experienced hands (and strong flour).

Higher hydration is not "better" — it's a trade-off between crumb openness and handleability. A well-fermented 70% loaf beats a mishandled 85% one every single time. Fermentation timing matters more than water: if you're not yet confident reading your starter, start with when it peaks.

Your flour sets the limit

The number on the recipe assumes the author's flour. Yours is different. Protein percentage is only half the story — quality matters as much as quantity: some 11.5% protein flours drink 83% hydration gracefully, while some 13% flours struggle at 78%. Whole-grain flours absorb far more water than white flours.

Practical rule: when trying a new flour, drop the recipe's hydration by about 5 points, watch how the dough behaves, and work back up over the next bakes. Getting to know one flour deeply beats hopping between five.

Water quality: the one thing to check

Most tap water is fine, with one exception: chlorine, which is there to kill microorganisms and doesn't spare your starter's yeast. The fix is free — let the water sit uncovered for 30 minutes to overnight and the chlorine evaporates. Filtered or spring water works too. Water hardness has a mild effect (very hard water tightens gluten, very soft water slackens dough), but don't overthink it unless you're troubleshooting a persistent problem.

Scaling any recipe

Baker's percentages make scaling trivial. Want two loaves instead of one? Keep the percentages and multiply the flour; everything else follows. Want the same recipe at 72% instead of 78% for a hot, humid day? Multiply flour weight by 0.72 and that's your water target.

The Levain app does this arithmetic for you: a hydration calculator that accounts for the starter's contribution, and recipes that rescale live when you change the dough size.