Sourdough Hydration Calculator
Most recipes give hydration as water ÷ flour and leave out the starter. This calculator splits the starter into its flour and water, so you get the true hydration of the dough, the water to add for the hydration you want, and a full recipe from a target dough weight.
Check a recipe
Enter the amounts in grams as the recipe gives them.
Build a recipe from dough weight
Choose the dough weight and percentages. Starter % is the starter weight ÷ the flour you add, the way most recipes write it.
Quick answer: water to add for a target hydration
For 500 g flour, 100 g starter at 100% hydration (50 g flour + 50 g water inside it) and 11 g salt. Total flour = 550 g.
| True hydration | Water to add (g) | Dough weight (g) |
|---|---|---|
| 65% | 307.5 | 919 |
| 70% | 335.0 | 946 |
| 75% | 362.5 | 974 |
| 80% | 390.0 | 1,001 |
| 85% | 417.5 | 1,029 |
How starter hydration changes the dough
100 g of starter added to 500 g flour and 350 g water.
| Starter hydration | Flour in starter (g) | Water in starter (g) | True dough hydration |
|---|---|---|---|
| 50% | 66.7 | 33.3 | 67.6% |
| 75% | 57.1 | 42.9 | 70.5% |
| 100% | 50.0 | 50.0 | 72.7% |
| 125% | 44.4 | 55.6 | 74.5% |
How true hydration works
Hydration is the weight of water divided by the weight of flour, in baker's percentages. A sourdough starter is itself flour and water, so it changes both numbers. A starter at 100% hydration is half flour and half water by weight; a stiff starter at 50% hydration is two parts flour to one part water. When you add the starter's flour and water to the dough's, you get the true (total) hydration, which is what decides how slack or stiff the dough feels.
Formulas
Worked example 1: what is the real hydration of my recipe?
A recipe uses 500 g flour, 350 g water, 100 g starter at 100% hydration and 10 g salt. The recipe calls it 70% hydration (350 ÷ 500). The starter adds 50 g flour and 50 g water, so total flour is 550 g and total water 400 g. True hydration = 400 ÷ 550 = 72.7%. The starter is 20% of the added flour, 9.1% of all flour is prefermented in the starter, and the salt is 1.8% of the total flour. To reach 75% true hydration you need 0.75 × 550 − 50 = 362.5 g of water, which is 12.5 g more than the recipe. These numbers load in the first calculator.
Worked example 2: a 900 g loaf at 75%
With 75% hydration, 2% salt, 20% starter and a 100% hydration starter: total flour = 900 ÷ (1 + 0.75 + 0.02) = 508.5 g. Added flour = 508.5 ÷ (1 + 0.20 ÷ 2) = 462.2 g, starter = 20% of that = 92.4 g (46.2 g flour + 46.2 g water), water = 0.75 × 508.5 − 46.2 = 335.1 g and salt = 2% × 508.5 = 10.2 g. The four weights add up to 900 g. These numbers load in the second calculator.
Choosing a hydration
Lower hydration gives a dough that is easier to shape and a tighter crumb; higher hydration gives a slacker dough and a more open crumb, but it needs more strength from folds. Whole wheat and rye flours absorb more water than white flour, so the same hydration feels stiffer with them. A common salt level is 2% of the flour weight, as in the King Arthur baker's percentage example (1 lb salt to 50 lb flour). For the starter feeding schedule and time to peak, use the sourdough starter feeding calculator; for flour blends and other breads, use the bread baker's calculator.
Frequently asked questions
Does sourdough starter count toward hydration?
Yes, if you want the true hydration. A starter at 100% hydration is half flour and half water, and both go into the dough. Recipes often quote hydration without the starter, so the true value is usually 1–3 points higher.
How do I calculate the hydration of a starter?
Divide the water by the flour in the last feeding. 50 g flour and 50 g water is 100%. 50 g flour and 25 g water is 50%.
How much water should I add for 75% hydration?
Multiply the total flour (added flour + starter flour) by 0.75 and subtract the water already in the starter. For 500 g flour and 100 g starter at 100%: 0.75 × 550 − 50 = 362.5 g.
What is prefermented flour?
The share of the total flour that is already fermented in the starter or levain. In example 1, 50 g of 550 g is about 9%. More prefermented flour usually means faster fermentation.
Is salt part of the hydration?
No. Salt is counted as its own baker's percentage of the total flour. It adds to the dough weight but not to the hydration.
Sources
- King Arthur Baking, Baker's Percentage: flour is 100% and every other ingredient is a percent of the flour weight; the example uses 66% water and 2% salt.
- All other numbers on this page are computed from the formulas above by this calculator.
Estimates for home cooking, not medical or dietary advice. Brands, cuts and cooking methods change the real values.
Related tools
More calculators from RecipeTool that work with this one.