Sourdough recipes are ratios, and the ratio that matters most — hydration — is easy to get wrong when a starter full of flour and water joins the bowl. This calculator uses baker's percentages on the whole dough: pick the loaf size, the hydration you want, how much starter, and how wet your starter is, and it gives the exact grams to weigh, with the starter's share already subtracted.
Checking an existing recipe? The bread hydration calculator works out any dough's true hydration from its ingredients. Baking with commercial yeast instead, or making pizza? Try the yeast converter and the pizza dough calculator. Our guide to baker's percentages and the starter trap shows why the starter's flour and water count toward hydration, and for cakes, the cake pan converter scales a recipe to a new pan.
Frequently asked questions
How do I calculate sourdough hydration with a starter?
Count the starter’s flour and water in the totals. A starter at 100 % hydration is half flour and half water by weight, so 100 g of starter adds 50 g of each. Hydration is total water ÷ total flour. This calculator works that way: you enter the overall hydration you want, and it subtracts the starter’s flour and water from what you weigh out. For example, a 1,000 g loaf at 75 % with 20 % starter and 2 % salt needs about 508 g flour, 367 g water, 113 g starter, and 11 g salt.
What does starter percentage mean?
It is the starter weight as a percentage of flour, but recipes measure it two ways. Some divide by the total flour including the flour inside the starter; others divide by only the flour you add to the bowl, so “100 g starter to 500 g flour” is 20 %. The toggle lets you match your recipe. Typical amounts are 15–25 % for a same-day or overnight bulk ferment, and 5–10 % for a long, cool ferment. More starter means faster fermentation and a tangier loaf.
What if my starter is not 100 % hydration?
Enter its real hydration. A stiff starter at 50 % is two parts flour to one part water, so the same 100 g adds about 67 g flour and 33 g water. The calculator splits the starter accordingly, so the overall hydration stays exactly what you asked for. If the starter would bring more water than the whole dough is allowed — for example a very high starter percentage in a low-hydration dough — you will see a message asking you to adjust the numbers.
How do I use the “I have this much starter” mode?
Switch the mode and type how much ripe starter you have. The calculator treats that as the starter percentage of the flour and builds the rest of the recipe around it, reporting the total dough and the weight per loaf. It is handy when your starter jar decides the batch size. Remember to keep a spoonful back to feed, or you will be building a new starter from scratch. The starter percentage and basis still apply in this mode, so a smaller percentage stretches the same starter into a bigger batch of dough, with a slower rise.
What hydration should a beginner use for sourdough?
Around 68–72 % with white bread flour is forgiving: the dough is sticky but shapes well. Many classic country loaves sit around 75 %, and open-crumb loaves go to 80 % or more, which needs confident shaping and strong flour. Whole-wheat and rye flours absorb more water, so a whole-grain loaf can feel stiffer at the same number — raise hydration by 5–10 points as the whole-grain share grows. If a new recipe feels too slack to shape, hold back about 5 % of the water and add it during the first set of folds once you know how the flour behaves.