How do you calculate sourdough hydration?
Hydration is the weight of water divided by the weight of flour. For sourdough, count the flour and water inside your starter too. Split the starter by its own hydration, add its flour to your flour and its water to your water, then divide total water by total flour.
True hydration = (water + starter water) ÷ (flour + starter flour)
Starter flour = starter ÷ (1 + starter hydration)
Starter water = starter − starter flour
Worked example
These are the calculator's default numbers: a simple country loaf.
- You add 500 g flour, 350 g water, 100 g starter and 10 g salt. The starter is fed with equal weights of flour and water, so its hydration is 100 %.
- Split the starter: 100 ÷ (1 + 1) = 50.0 g flour, and the other 50.0 g is water.
- Total flour: 500 + 50 = 550 g. Total water: 350 + 50 = 400 g.
- True hydration: 400 ÷ 550 = 72.7 %.
- Water ÷ flour without the starter would say 70.0 %. The gap of almost three points is the starter.
- Salt is 1.8 % of total flour, and the starter is 18.2 % of total flour (20.0 % of the flour you added).
Why your starter changes hydration
Starter is just flour and water that has been fermenting. When you mix it into a dough, both parts end up in the bread. A recipe that lists "500 g flour, 350 g water, 100 g starter" is not a 70 % dough. How far off it is depends on how much starter you use and how wet it is.
A 100 % starter is wetter than most doughs, so it pushes hydration up. A stiff starter, fed with half as much water as flour, is drier than most doughs and pulls hydration down. The table keeps 500 g flour and 350 g water and changes only the starter.
| Starter | 100 % starter | 50 % (stiff) starter |
|---|---|---|
| None | 70.0 % | 70.0 % |
| 50.0 g | 71.4 % | 68.8 % |
| 100 g | 72.7 % | 67.6 % |
| 150 g | 73.9 % | 66.7 % |
| 200 g | 75.0 % | 65.8 % |
With no starter both columns read 70.0 %. With 200 g of liquid starter the same recipe is a 75.0 % dough, and with 200 g of stiff starter it is 65.8 %. That is enough to change how the dough handles.
Grams for a 1 kg dough at 65 to 80 % hydration
Use "Plan a dough" for any weight. The table shows a 1,000 g dough with 20 % starter (of total flour), a 100 % starter and 2 % salt. The hydration here is true hydration, starter included.
| Hydration | Flour | Water | Starter | Salt |
|---|---|---|---|---|
| 65.0 % | 539 g | 329 g | 120 g | 12.0 g |
| 70.0 % | 523 g | 349 g | 116 g | 11.6 g |
| 75.0 % | 508 g | 367 g | 113 g | 11.3 g |
| 80.0 % | 495 g | 385 g | 110 g | 11.0 g |
Starter %: of total flour or of added flour?
Recipes write the starter amount in two ways, and they give different numbers for the same dough. In the worked example, 100 g of starter is 18.2 % of the total flour (550 g) but 20.0 % of the flour you add (500 g). Neither is wrong. Check which one your recipe means, and pick the same one under "Starter % is of" when you plan a dough. In "I have amounts" mode the calculator shows both.
Grams, ounces and cups
The calculator works by weight. A cup of flour can weigh quite different amounts depending on how it is scooped, so cups make hydration guesswork. Ounces work fine: switch the units under the calculator and every weight converts. For water, 1 ml weighs close enough to 1 g for baking, so a measuring jug in millilitres also works.
You can type numbers with a comma or a point. "2,5" and "2.5" both mean two and a half. When a number has a separator, the calculator shows how it read it under the field, so "1,000" never turns into 1 by mistake.
Questions
Does the starter count toward hydration?
Yes. The starter's water and flour are part of the dough. Leaving them out is the most common reason a dough feels wetter or drier than its recipe says. That is the number this calculator puts first.
What hydration should I start with?
Follow your recipe's number if it has one. Lower hydration is easier to shape. For reference, King Arthur's baker's percentage guide uses 66 % for a white bread and 73 % for ciabatta. Higher numbers give a more open crumb but a stickier dough.
How do I find my starter's hydration?
Look at how you feed it. Equal weights of flour and water, say 50 g of each, is a 100 % starter. 50 g water with 100 g flour is a 50 % (stiff) starter. If you feed by cups or spoons, weigh one feed once and use that.
Does salt change the hydration?
No. Hydration only compares water and flour. Salt is shown as a percentage of total flour, usually around 2 %, so you can check it next to your recipe.
What about milk, eggs or oil?
This calculator only counts water. Milk is mostly water and eggs contain a lot of it, but they also add fat and protein that change how the dough feels. Enter only the water if you want a hydration you can compare with other lean sourdough recipes.
Why does my dough feel wetter than the number says?
Flours absorb different amounts of water. Whole wheat and fresh-milled flour soak up more than white bread flour, so the same hydration can feel stiff with one and slack with another. The number tells you the recipe. Your hands tell you the flour.
Sources
- King Arthur Baking: Baker's percentage: hydration as water weight over flour weight, and the 66 % white bread and 73 % ciabatta examples.
- The starter split and the reverse "plan a dough" formulas are standard baker's math, written out above. Every number on this page is calculated by the same code as the calculator.