How to Calculate Sourdough Hydration Percentage: Formula, Starter Math & Chart

Sourdough hydration is (total water ÷ total flour) × 100, and both totals must include the flour and water already inside your starter. A dough with 500 g flour, 375 g water, and 100 g of 100%-hydration starter has 550 g flour and 425 g water total — 77.3% hydration. Skip the starter's share and you'll under-hydrate by several points. Get your exact water amount in our free sourdough hydration calculator; the worked math is below.

The formula: total water ÷ total flour × 100

Sourdough hydration is a baker's percentage: hydration % = (total water weight ÷ total flour weight) × 100, with flour always treated as 100%. A dough made from 500 g flour and 350 g water is 70% hydration — simple. The part most recipes gloss over is the word total: the water and flour already inside your starter count. A starter is just flour and water that fermented early, and ignoring it is the single most common hydration error. Weigh everything in grams — hydration math collapses if you use cups, because a 'cup of flour' can vary by 30% depending on how you scoop it. If your recipe is in volume units, convert first with our grams to ounces converter, then do the hydration math in grams. Once the formula is in weights, every hydration question becomes one division.

Does the starter count? Yes — here's the math

A 100 g starter at 100% hydration (equal weights flour and water) contains 50 g flour and 50 g water. Add that to your dough's flour and water before dividing. Worked example: 500 g flour + 375 g water + 100 g starter at 100% hydration. Total flour = 500 + 50 = 550 g. Total water = 375 + 50 = 425 g. Hydration = 425 ÷ 550 × 100 = 77.3%. If you had ignored the starter, you would have calculated 375 ÷ 500 = 75% — nearly two and a half points low, enough to change the crumb from open to merely airy. The error grows with bigger levains: a recipe using 200 g of starter at 100% hydration hides 100 g of flour and 100 g of water, and skipping it throws the result off by four or more points. Rule of thumb: if your starter is more than ~15% of the flour weight, starter-inclusive math is not optional.

Worked example: building a 75% dough from scratch

Most bakers work backwards: pick a target hydration, then solve for the water to add. Say you want 75% hydration with 500 g flour and 100 g of 100%-hydration starter. Step 1: total flour = 500 + 50 (starter's flour) = 550 g. Step 2: target water = 0.75 × 550 = 412.5 g. Step 3: the starter already contributes 50 g of water, so water to add = 412.5 − 50 = 362.5 g. Mix 500 g flour + 362.5 g water + 100 g starter (+ 10 g salt, which at 2% of total flour weight does not count toward hydration) and you hold exactly 75%. Check: (362.5 + 50) ÷ 550 = 0.75 ✓. One more useful inversion: if a recipe gives you a finished dough weight and a hydration, flour = dough weight ÷ (1 + hydration). A 1,000 g dough at 75% hydration contains 1,000 ÷ 1.75 ≈ 571 g flour and 429 g water — handy when scaling recipes up or down.

Sourdough hydration chart: what the numbers mean

Hydration decides handling and crumb more than any other variable. 60–65% (stiff): firm dough, easy to shape, tight even crumb — bagels and sandwich loaves live here. 65–70% (everyday): soft but manageable, the beginner sweet spot for boules; open-ish crumb with holes. 70–75% (artisan): slack dough needing folds and confident shaping; this is the classic open-crumb range. 75–80% (high): wet dough, sticky hands, big irregular holes — rewarding but unforgiving. 80%+ (very high): ciabatta and focaccia territory; more batter than dough, baked in pans or with expert handling. Higher hydration also ferments faster (water mobilizes enzymes and yeast), so a 78% dough can over-proof while a 68% dough with the same starter is still rising. Beginners should master 68–70% before chasing 78%: an open crumb at 70% with good fermentation beats a gummy 80% loaf every time.

Stiff starters and whole grains change the math

Not every starter is 100% hydration. A stiff starter at 50% hydration (half as much water as flour) splits differently: 100 g of 50%-hydration starter = 66.7 g flour + 33.3 g water (flour = 100 × 100/150, water = 100 × 50/150). General formula: starter flour = starter weight × 100/(100 + starter hydration); starter water = the rest. Run the main example with a stiff starter: 500 g flour + 375 g water + 100 g starter at 50% → total flour 566.7 g, total water 408.3 g → 72.1% hydration, five points lower than with a liquid starter. Whole grains shift things the other way: whole wheat and rye absorb 5–10% more water than white flour, so a 75% white-flour recipe needs ~80% hydration to handle the same with whole wheat. Our free sourdough hydration calculator handles both adjustments automatically — enter your starter's hydration and flour blend, and it returns the exact water to add.

5 mistakes that throw off your hydration

1. Ignoring the starter's water. Covered above — the most common error, worth 2–5 points. 2. Measuring flour by volume. A cup of flour weighs 120–150 g depending on scooping; at 500 g of flour that is a ±10% hydration swing from measuring alone. Weigh everything. 3. Counting salt as hydration. Salt (standard 2% of total flour weight — 10 g per 500 g flour) dissolves into the water but is not water; leave it out of the division. 4. Chasing high hydration too early. Wet dough magnifies every shaping mistake; a well-fermented 70% loaf outscores a collapsed 80% one. 5. Forgetting the flour blend. Swapping 20% of white flour for whole wheat without adding water silently drops effective hydration by ~2 points — the dough feels stiffer than the number suggests. Fix any one of these and your hydration numbers start predicting your crumb instead of surprising you.

Baking math, made instant

Hydration is one division, but it sits inside a web of baking conversions — grams to ounces for American recipes, milliliters to ounces for liquids, cups to grams for flour. Our grams to ounces converter and ounces to grams converter handle the weight swaps; recipes that list water or milk in fluid ounces convert through our fluid ounces to liters converter, and the free unit converter covers the rest. For the hydration itself, skip the arithmetic: the free sourdough hydration calculator takes your flour, starter weight, starter hydration, and target, then returns the exact water to add plus a full baker's-percentage table. Find every tool from the ToolNest homepage. Related guides: grams to ounces formula, milliliters to ounces, and tablespoons to cups.