How to calculate sourdough hydration with starter
Total hydration is all the water divided by all the flour, including the water and flour in your starter or levain. A recipe's added-water-to-added-flour ratio can give a different percentage.
This calculator plans how much water to add for your chosen target total hydration. Set added flour or total dough weight, then enter starter mass and starter hydration. To check an existing recipe, use the total-hydration formula below.
The complete hydration formula
Let F be added flour in grams, W added water in grams, S starter mass in grams, and h starter hydration as a percentage.
- Starter flour
- S ÷ (1 + h ÷ 100)
- Starter water
- S − starter flour
- Total hydration (%)
- 100 × (W + starter water) ÷ (F + starter flour)
- Water to add for a target (%)
- (target ÷ 100) × (F + starter flour) − starter water
A 100% hydration starter has equal flour and water by weight. A 50% hydration starter has half as much water as flour; 100 g of it contains about 66.67 g flour and 33.33 g water.
To calculate what your sourdough starter contains after feeding, or to find its hydration from an unequal flour and water feed, use our Starter Hydration Calculator.
Same recipe, two starter hydrations
Both examples keep added flour at 500 g, added water at 350 g and starter mass at 100 g. Only starter hydration changes.
| Starter hydration | Starter flour | Starter water | Total water ÷ total flour | Total hydration |
|---|---|---|---|---|
| 100% | 50 g | 50 g | 400 g ÷ 550 g | 72.73% |
| 50% | 66.67 g | 33.33 g | 383.33 g ÷ 566.67 g | 67.65% |
Ignoring starter gives 350 ÷ 500 = 70% in both cases. The complete ratios use the unrounded starter breakdown. The table shows two decimals; calculator cards show one decimal.
Downloadable worked-example handout & reference data
Download the free 2-page educational worked-example handout (PDF) or the unrounded reference dataset (CSV) for kitchen, study, or classroom use. Each page covers one case with full algebraic steps, comparison against the 70% shorthand, and a blank worksheet to calculate your own formula.
Printable 2-page lesson covering 100% and 50% starter breakdowns, unrounded fractions, and blank calculation grid.
CSV · SpreadsheetDownload Worked Examples Dataset (CSV)Precise reference data with exact unrounded numbers, algebraic formulas, and multi-decimal comparison columns.
These materials are strictly educational mathematical examples, not bake results, expert validation, or hydration recommendations. Flour blend and salt apply to added flour only; they are omitted from the teaching math to focus on the total water-to-flour ratio.
Compare target hydration without changing the starter
With 500 g added flour and 100 g of 100% hydration starter, total flour is 550 g and the starter supplies 50 g water:
- 65% target: 307.5 g water to add.
- 70% target: 335 g water to add.
- 75% target: 362.5 g water to add.
These are arithmetic scenarios, not recommended hydration levels. Flour type, absorption, mixing and the bread you want affect which target works for you.
Calculation notes and sources
Only flour and water enter the hydration ratio. This tool calculates salt as a percentage of added base flour, as shown beside the Salt input. Flour blend percentages also apply to added flour; the starter's flour is counted separately.
The tool does not adjust water for eggs, milk or other ingredients. It cannot infer your starter hydration from its appearance. A target that requires negative added water is rejected; all calculations remain entirely in your browser. Recipe inputs are processed locally on your device. Save on this device uses local browser storage.
Method reference: King Arthur Baking on bread hydration and counting starter flour and water. Worked examples above are calculated for this page, not measured baking trials.