What dough hydration means
Hydration is the water in a dough as a percentage of the flour, by weight. It is one of the baker's percentages, the way bakers write formulas: the flour is always 100% and every other ingredient is a percentage of the flour weight. 375 g of water on 500 g of flour is 75% hydration, and 10 g of salt on the same flour is 2% salt. Because everything is relative to the flour, the same percentages work for one loaf or for twenty.
Why the starter changes the number
A sourdough starter, or the levain you build from it, is nothing but flour and water that have fermented. Once it goes into the dough, its flour and its water are part of the dough like everything else. If you only divide the water you pour by the flour you weigh, you leave them out and the number comes out wrong.
Example: 450 g of flour, 325 g of water, 100 g of starter at 100% hydration and 10 g of salt. Without the starter, the dough looks like 325 ÷ 450 = 72.2% hydration. The starter adds 50 g of flour and 50 g of water, so the real dough has 500 g of flour and 375 g of water: 75% hydration. The gap grows with the amount of starter and with how far the starter's hydration is from the dough's. A starter wetter than the dough raises the real hydration, a stiffer one lowers it.
King Arthur Baking's guide to baker's percentage handles a preferment the same way, in its example a poolish of equal weights of flour and water. For formulas with a preferment it suggests also writing an overall baker's percentage, based on the sum of all the flour and all the water. In its own example, a poolish French bread lists 48% water in the final mix but works out to 65% overall once the flour and water of the poolish are added in. The calculator gives you that overall number.
Starter hydration
Starter hydration is the water in the starter as a percentage of its flour. Fed with equal weights of flour and water, a starter is at 100% and splits half and half. A stiff starter fed with 50 g of water per 100 g of flour is at 50%: of 150 g of it, 100 g is flour and 50 g is water. A liquid starter at 125% holds 125 g of water per 100 g of flour. Enter what you feed your starter with, and the calculator does the split.
Baker's percentages of the whole dough
The result lists every ingredient as a percentage of the total flour, the flour you add plus the flour inside the starter. For the example above that looks like this:
| Ingredient | Weight | Baker's % |
|---|---|---|
| Flour | 450 g | 90% |
| Water | 325 g | 65% |
| Starter (100%) | 100 g | 20% |
| Salt | 10 g | 2% |
| Total flour | 500 g | 100% |
| Total water | 375 g | 75% |
Recipes do not all write the starter the same way. Some give it as a share of the total flour, as here (20%), others as a share of the flour added in the final mix (100 ÷ 450 = 22.2%). The calculator shows both, so you can match the recipe you follow.
Planning a dough for a target hydration
Plan a dough works backwards. You choose the total flour, the hydration you want, how much starter to use and how much salt, and the calculator tells you what to weigh. It first works out the starter weight from the total flour, then subtracts the flour and water in the starter from the totals, so the finished dough lands exactly on your target.
With 500 g of total flour, 75% hydration, 20% starter at 100% and 2% salt you get the same dough as above: 450 g of flour, 325 g of water, 100 g of starter and 10 g of salt. If the starter alone holds more water than the target allows, which happens with a lot of liquid starter and a low hydration, the calculator tells you to use less starter or a higher hydration.
Milk, eggs, butter and honey
Enriched doughs get part of their water from other ingredients. Open Milk, eggs and other extras to add them: the calculator counts the water inside each one, using the water content per 100 g listed in USDA FoodData Central, and shows the hydration with and without it. Their other parts, like milk solids or the fat in butter, add to the dough weight but not to the flour.
| Ingredient | Water per 100 g | USDA entry |
|---|---|---|
| Whole milk | 88.1 g | FDC 171265 |
| Whole egg | 76.2 g | FDC 171287 |
| Butter | 16.2 g | FDC 173410 |
| Honey | 17.1 g | FDC 169640 |
For anything else, use Other ingredient and type its water content yourself, from the label or a nutrition database. To scale a finished sourdough recipe up or down, the recipe scaler multiplies every line, and for pizza dough with yeast the pizza dough calculator works with the same baker's percentages.
How to use the sourdough hydration calculator
- 1Choose Check my dough to analyze a recipe, or Plan a dough to start from a target hydration, then pick grams or ounces.
- 2Enter the flour, water, starter and salt, or the total flour and the percentages, and the hydration of your starter.
- 3Read the hydration and the baker's percentages, or the amounts to weigh, and copy the result for your bake.
Frequently asked questions
What is sourdough hydration?
Hydration is the weight of the water in a dough divided by the weight of the flour, as a percentage. 375 g of water on 500 g of flour is 75% hydration. For sourdough the honest number counts the flour and water inside the starter too, which is what this calculator does.
Does the starter count toward hydration?
Yes. A starter is just flour and water, so both end up in the dough. A 100% hydration starter is half flour and half water by weight: 100 g of it adds 50 g of flour and 50 g of water. Leaving it out gives the wrong number: a 100% starter in a dough below 100% hydration makes the dough wetter than the recipe seems to say.
What does starter hydration mean?
It is the water in your starter as a percentage of the flour in it. A starter fed with equal weights of flour and water is at 100%. One fed with 50 g of water for every 100 g of flour is at 50%, a stiff starter: two thirds of its weight is flour and one third is water.
What does the starter percentage mean here?
In this calculator the starter percentage is the starter weight as a share of the total flour, the flour you add plus the flour inside the starter. 100 g of starter in a dough with 500 g of total flour is 20%. Some recipes compare the starter with the added flour only, so check what your recipe means; the calculator shows both.
Does milk count as water in the hydration?
Milk is mostly water. USDA FoodData Central lists whole milk at 88.1 g of water per 100 g, a whole raw egg at 76.2 g, salted butter at 16.2 g and honey at 17.1 g. The calculator adds that water to the hydration when you enter these extras, and shows the hydration without them too.
Is salt part of the hydration?
No. Hydration compares only water with flour. Salt still gets its own baker's percentage, the salt weight divided by the total flour, and it counts toward the total dough weight.