How to use the sourdough hydration calculator
- Choose Find the hydration to check a recipe, or Find the water to add to hit a target.
- Enter the flour added to the dough, and the water added (or the target hydration).
- Enter the starter added and its hydration. A starter fed with equal weights of flour and water is 100 percent. Open More options to add salt.
- Read the overall hydration, the flour and water inside the starter and the totals for the whole dough.
Formula
Starter flour = starter / (1 + starter hydration)
Starter water = starter - starter flour
Hydration = (water added + starter water) / (flour added + starter flour)
Water to add = (flour + starter flour) x target - starter water
A 100 percent hydration starter is half flour and half water by weight. A stiffer starter holds less water, so its hydration is lower.
500 g flour, 350 g water and 100 g of starter
A 100 percent starter of 100 g holds 50 g of flour and 50 g of water. Total flour is 550 g and total water is 400 g, so the overall hydration is 400 / 550 = 72.7 percent, not the 70 percent you get by ignoring the starter. The starter is 18.2 percent of the total flour, 10 g of salt is 1.82 percent, and the dough weighs 960 g.
To reach 72 percent with the same flour and starter, add 346 g of water. With a stiffer starter at 60 percent hydration, 400 g flour, 300 g water and 80 g starter give 73.3 percent: the starter holds 50 g of flour and 30 g of water. With 1,000 g flour and 200 g of an 80 percent starter, a 75 percent target needs 744.4 g of water.
Why the starter counts
A starter is flour and water that have been fermenting together, so when you add it to a dough you add both. If you leave it out of the sum, a dough with a lot of starter will be wetter than its stated hydration. Bakers who work in percentages count the starter's flour and water in the totals, which is what this tool does. That is also why the starter as a share of total flour is shown: it describes how much of the dough is already fermented.
To express every ingredient as a percent of the flour, use the Baker's Percentage Calculator. For a commercial yeast preferment, the Poolish and Biga Calculator splits the flour and water the same way.
Reading the result
A higher hydration usually means a softer, stickier dough and a more open crumb, and a lower one a firmer dough that is easier to shape. How a given number feels depends on the flour, its protein and how it absorbs water, so treat the figure as a starting point and adjust by feel. If the starter already brings more water than your target allows, the tool says so instead of showing a negative amount. For yeast measures in a different form, the Yeast Conversion Calculator can help.
Assumptions and limits
- The starter is made only of flour and water, and its hydration is the number you enter.
- All amounts are in grams.
- Salt is shown as a share of total flour but does not change hydration.
- The calculation runs in your browser and stores nothing.
Frequently asked questions
How do I calculate the hydration of a sourdough with starter?
Split the starter into its flour and water, add those to the flour and water you mix in, and divide total water by total flour. For 100 g of 100 percent starter, add 50 g to both.
What is the hydration of my starter?
It is the weight of water divided by the weight of flour in your starter. Feeding with equal weights gives 100 percent, and less water gives a lower number.
Why is my total hydration higher than my recipe says?
Because the recipe may list only the water added to the dough. The starter's own water pushes the real hydration up, which this tool shows.
What if the target is too low?
If the starter already holds more water than the target allows, no water can be added to reach it. Use less starter or raise the target hydration.