The formula
Hydration is total water divided by total flour. A 100% hydration starter is half flour and half water by weight, so 100 g of starter adds 50 g of each.
hydration = (water + starter water) ÷ (flour + starter flour) × 100
What the numbers feel like
- 60–68%: firm, easy to shape, good for bagels and sandwich loaves.
- 68–75%: the classic home-baker range for open-crumb country loaves.
- 75%+: slack and sticky; great crumb, harder to handle. Whole-grain flours absorb more water, so they feel stiffer at the same number.