Sourdough Hydration Calculator
Flour, water and starter in — true hydration out. Or set a target and get the water to add.
Starter counts toward the totals: a 100% starter is half flour, half water by weight.
What is dough hydration?
Hydration is the weight of water in a dough expressed as a percentage of the weight of flour. Mix 500 g of flour with 350 g of water and you have a 70% hydration dough. Bakers use this convention — baker’s percentages, where flour is always 100% — because it makes recipes scalable: the ratio describes the dough no matter how big the batch is.
Why the starter changes the number
A sourdough starter is itself made of flour and water, so it has to be counted. A starter kept at 100% hydration is half flour and half water by weight: add 100 g of it to your dough and you have really added 50 g of flour and 50 g of water. Ignore that and your “70% dough” can be several points wetter or drier than you think — which is exactly why two bakers following the same recipe sometimes end up with very different doughs. This calculator folds the starter into the totals for you.
What hydration should I aim for?
There is no single right answer, but the ranges are well established. Around 60–68% gives a firm, forgiving dough that is easy to shape — the best place to learn. 70–75% is the classic sourdough range, balancing an open crumb with manageable handling. Above 78% the dough turns slack and sticky and rewards experience with coil folds and gentle shaping.
Flour matters as much as the number: wholegrain and strong bread flours absorb far more water than plain white flour, so an 80% wholemeal dough can feel drier than a 72% white one. Treat the percentage as a starting point, adjust by feel, and keep notes on what each flour can take.
How it works
The calculator first splits your starter into the flour and water it contains. A starter kept at a hydration of h% holds flour equal to its weight × 100 ÷ (100 + h), and water equal to its weight × h ÷ (100 + h). Those amounts are added to the flour and water you weigh out, and hydration is total water divided by total flour, multiplied by 100.
Working backwards is the same sum rearranged. To reach a target, the water to add is that percentage of the total flour, minus the water the starter is already carrying.
A worked example
Take a common formula: 500 g of flour, 350 g of water and 100 g of starter at 100% hydration. On paper, 350 over 500 looks like a 70% dough.
| Flour inside the starter (100 × 100 ÷ 200) | 50 g |
| Water inside the starter (100 × 100 ÷ 200) | 50 g |
| Total flour (500 + 50) | 550 g |
| Total water (350 + 50) | 400 g |
| True hydration (400 ÷ 550 × 100) | 72.7% |
The dough is nearly three points wetter than the recipe suggests. To bring it back to a true 70%, work backwards: 70% of 550 g is 385 g of water, less the 50 g the starter supplies, which leaves 335 g to add.
Frequently asked questions
How do I calculate sourdough hydration?
Divide the total weight of water by the total weight of flour and multiply by 100 — counting the flour and water inside your starter as well as what you weigh out. A 100% starter is half flour and half water, so 100 g of it adds 50 g of each.
Does the starter count towards hydration?
Yes. Starter is flour and water, so leaving it out understates both totals. With a generous amount of starter the difference can be several percentage points, which is enough to change how the dough handles.
What hydration should a beginner use?
Somewhere between 60% and 68% with white bread flour. The dough is firm enough to shape without sticking to everything, and still bakes into a good loaf. Once shaping feels comfortable, move up a few points at a time.
What if my starter is not 100% hydration?
Enter its actual hydration in the starter field. A stiff starter at 50% hydration is two-thirds flour and one-third water, so it adds more flour and less water to the dough than a liquid starter of the same weight. The calculator adjusts both totals for you.
Does water added later, such as with the salt, count?
Yes. Hydration describes the finished dough, so any water that ends up in it counts — including water held back and worked in later with the salt. Add it to the water figure before you calculate.
A free web tool from the makers of The Bake Log — starter feeding reminders, guided bake timelines and a full bake journal. Offline, no account, free to start.
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