Sourdough Calculator: Starter, Flour, Water and Salt
Sourdough calculator
Enter the dough you want and your formula's baker's percentages. The calculator counts the flour and water already inside your starter, so the final hydration is the one you asked for.
Count the starter's flour and water in your totals. For a 900 g loaf at 70% hydration and 2% salt with 10% prefermented flour (100% starter), use about 105 g starter, 471 g flour, 314 g water and 10 g salt.
| Prefermented flour | Starter | Flour to add | Water to add | Salt |
|---|---|---|---|---|
| 10% | 105 g | 471 g | 314 g | 10 g |
| 15% | 157 g | 445 g | 288 g | 10 g |
| 20% | 209 g | 419 g | 262 g | 10 g |
Example: a 900 g loaf at 70% hydration
The starter is part of the dough
A sourdough starter is flour and water. When a formula says "70% hydration", it normally means the total water in the dough, including the water inside the starter, divided by the total flour, including the flour inside the starter. If you add 150 grams of starter on top of a recipe that already balances flour and water, the dough ends up wetter and heavier than intended. The calculator does that bookkeeping for you.
The method follows the baker's percentages explained by King Arthur Baking: every ingredient is expressed relative to total flour weight. Start from the dough weight you want, divide by one plus the hydration and salt percentages to get the total flour, then split flour and water between the starter and what you add to the bowl.
What "prefermented flour" means
Recipes describe the amount of starter in different ways: as a weight, as a percentage of the flour you add, or as the percentage of total flour that has already fermented in the starter. I use the last one in this calculator because it stays meaningful when the starter's own hydration changes. With 10% prefermented flour, one tenth of all the flour in the dough arrives inside the starter. If your recipe lists flour in cups, the cups to grams converter gives a weight to start from.
If your recipe gives starter as a percentage of the added flour instead, convert once: a 100% hydration starter at 20% of the added flour contains flour equal to 10% of the added flour, which is roughly 9% of total flour. When in doubt, compare the starter weight in your recipe with the calculator's result and adjust the percentage until they match.
Worked example
For a 900-gram loaf at 70% hydration with 2% salt, the total flour is 900 ÷ 1.72, about 523 grams, and the total water about 366 grams. At 10% prefermented flour with a 100% hydration starter, the starter holds 52 grams of flour and 52 grams of water, so it weighs about 105 grams. You add about 471 grams of flour, 314 grams of water and 10 grams of salt.
Change only the starter to a stiff 50% hydration starter and the flour you add stays the same, but the starter now weighs about 78 grams and you add about 340 grams of water. The final dough is still 70% hydration. That is the case where ignoring the starter's water makes the biggest difference.
Choosing the numbers
The calculator does not choose a hydration or a starter amount for you, and I think that is the right limit. Flour type changes how much water a dough can hold: whole grain flours usually absorb more than white bread flour. A higher starter percentage makes fermentation move faster, which matters more in a warm kitchen than a cool one. These are choices to take from a formula you trust, then adjust one at a time.
My suggestion for a new formula is to keep the hydration at the recipe's figure for the first few bakes and change the starter percentage only if the timing does not fit your day. Changing several numbers at once makes it hard to see which change helped.
Salt and small quantities
At 2%, salt is a small number, about 10 grams for this loaf. It is still worth weighing on a scale that reads single grams, because salt affects both flavor and fermentation. The calculator applies the salt percentage to total flour, including the flour in the starter, which is the usual baker's percentage convention.
Limits of this calculator
It covers flour, water, salt and starter. It does not add inclusions such as seeds, oil or a soaker, and it does not predict bulk fermentation or proofing time. If your formula includes other ingredients, add them as their own baker's percentages after checking how they affect the total weight. For yeasted pizza dough, use the pizza dough calculator.
FAQ
Does sourdough hydration include the starter?
In baker's percentage terms, yes: hydration is total water divided by total flour, and the starter contains both. This calculator includes them, so the hydration you enter is the hydration of the finished dough.
What is a 100% hydration starter?
A starter fed with equal weights of flour and water, for example 50 grams of each. A 50% hydration starter has half as much water as flour and is much stiffer.
How much starter should I use?
Follow your formula. The calculator turns its percentage into grams but does not choose one, because the right amount depends on your flour, kitchen temperature and schedule.
Why does the calculator refuse some settings?
If the starter would bring more water than the whole dough is allowed to contain, there is no water left to add. Lower the starter amount or raise the hydration.
Can I use it for yeasted bread?
It is built for a sourdough starter. For a flour, water, salt and commercial yeast dough, the pizza dough calculator handles the same arithmetic.
