What people use it for
- Checking a recipe Find out what the loaf you already bake really sits at, starter included.
- Fixing a wet dough See how much water to take out to bring it back to a shape you can handle.
- Scaling up Keep the same percentages when you go from one loaf to five.
Why the starter changes the number
A starter is flour and water that has already been mixed, so a 100 g starter kept at 100% hydration is 50 g of flour and 50 g of water, not 100 g of something neutral. Most recipes quote hydration as water divided by flour and forget to say which side the starter lands on. This calculator splits the starter by its own hydration and adds each half to the right total, which is the only way the percentage on the page matches the dough in the bowl.
The same split decides the salt. Salt is measured against total flour, so 10 g of salt in a dough with 550 g of flour is 1.8%, not the 2% the packet suggests. That difference is what makes a loaf taste flat on one day and right on the next.
Working to a target instead of guessing
When you know the hydration you want, the last row does the subtraction for you: it takes the total flour, works out the water that percentage asks for, and says how many grams to add or pour off. Upping a dough from 72% to 78% is a few grams at a time, and doing it by feel is how a dough turns from firm to unworkable in one pour.
| Flour | Water | Starter at 100% | True hydration |
|---|---|---|---|
| 500 g | 300 g | 100 g | 66.7% |
| 500 g | 350 g | 100 g | 72.7% |
| 500 g | 400 g | 100 g | 78.8% |
| 1000 g | 700 g | 200 g | 72.7% |