How baker's hydration works
Hydration is the weight of water in a dough divided by the weight of flour, written as a percentage. A dough made with 500 g of flour and 375 g of water is at 75% hydration — the water is 75% of the flour's weight, not 75% of the total. Working in baker's percentages like this lets you compare and scale recipes regardless of batch size: a 65% loaf behaves the same whether you mix one or ten.
Hydration is the single biggest lever on how a dough handles and how the crumb turns out. Lower hydration (55–62%) gives a stiff, easy-to-shape dough and a tight, even crumb — think bagels and sandwich bread. The mid-60s are the all-purpose range for a standard loaf. Push past 75% and the dough turns slack and sticky, but you're rewarded with the open, irregular holes of ciabatta and rustic sourdough. A 100% biga or poolish preferment uses equal weights of flour and water.
Because the three quantities are linked by one equation — water = flour × hydration — knowing any two gives you the third. This calculator solves in all three directions: set flour and hydration to get water, set flour and water to read off your actual hydration, or fix water and hydration to back into the flour you need. Weigh everything in grams for the cleanest math; the unit switcher handles ounces and pounds without rounding away precision.
One thing the percentage doesn't capture is flour type. Whole wheat, rye, and freshly milled flours drink far more water than white bread flour, so a 75% whole-grain dough feels stiffer than a 75% white one. If you're switching flours, treat your usual hydration as a starting point and add water by feel until the dough matches the texture you know.
Worked example
You're scaling a ciabatta to 1 kg of flour and want it at 80% hydration.
- Water = flour × hydration = 1000 g × 0.80
- Water = 800 g
→ 1000 g flour + 800 g water. Expect a wet, slack dough — handle with floured hands and a bench scraper.