Reading a dough by its hydration
Hydration — water as a percentage of flour weight — is the single most descriptive number in bread baking. Below about 65% you get stiff, easy-to-shape doughs: bagels, pretzels, sandwich loaves. 65–75% is classic artisan bread territory, workable by hand with a pleasantly open crumb. Above 75% doughs turn slack and sticky but reward you with the big irregular holes of ciabatta and high-hydration sourdough.
The power of baker's percentages is portability: a formula of 100% flour, 70% water, 2% salt, 1% yeast makes the identical bread whether you bake with 500 g of flour or 50 kg. That's why professional bakeries never write recipes any other way.
Note that whole-grain flours drink more water — a 75% whole wheat dough handles like a 68% white dough. And if your starter or preferment contains water, serious bakers count it toward total hydration.