Sourdough Hydration Calculator
Sourdough hydration is the water-to-flour ratio of the dough, but the starter is itself flour and water, so a naive ratio of added water to added flour is wrong. This calculator folds the starter's flour and water into the totals to give your true overall hydration. Enter your flour, added water, starter weight and the starter's own hydration, and it returns the true hydration percent along with the total flour and total water in the finished dough. Adjust water to hit your target hydration.
True hydration formula
starter water = starter * (h / (100 + h))
starter flour = starter * (100 / (100 + h))
total flour = flour added + starter flour
total water = water added + starter water
hydration % = total water / total flour * 100
Here h is the starter hydration percent. A 100 percent starter is half water and half flour, so a 100 g portion adds 50 g water and 50 g flour to the totals.
Worked example
- 500 g flour, 350 g water, 100 g of a 100 percent starter.
- Starter splits into 50 g water and 50 g flour.
- Total flour = 500 + 50 = 550 g; total water = 350 + 50 = 400 g.
- True hydration = 400 / 550 times 100 = 72.73 percent.
- Total dough weight is 950 g.
Sourdough hydration: frequently asked questions
What is dough hydration?
Hydration is the weight of water in a dough divided by the weight of flour, expressed as a percentage. A dough with 700 g water and 1,000 g flour is 70 percent hydration. Higher hydration gives a wetter, more open crumb; lower hydration gives a tighter, easier-to-handle dough.
Why does the starter affect hydration?
A sourdough starter is itself flour and water. A 100 percent hydration starter is half flour and half water by weight. To find true dough hydration you must add the starter's flour to your flour total and its water to your water total, then take the ratio. Ignoring the starter understates true hydration.
How do I split my starter into flour and water?
Use the starter's own hydration. For a starter at hydration h percent, the water fraction is h / (100 + h) and the flour fraction is 100 / (100 + h). A 100 percent starter is 50 percent water and 50 percent flour; a 50 g portion contributes 25 g water and 25 g flour.
What hydration should I aim for?
It depends on the bread and your skill. Beginner sourdough loaves are often 65 to 70 percent. Open, airy artisan loaves run 75 to 85 percent. Very high hydration over 85 percent is harder to shape. This calculator reports your true figure so you can adjust water to hit your target.
Official sources
- USDA FoodData Central: flour composition reference data.
- The formula is the standard baker's hydration ratio (water mass over flour mass), arithmetic by definition.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.