Sourdough Hydration Calculator ·
The short answer
Hydration is total water divided by total flour, multiplied by 100. Include both ingredients inside the starter. A recipe with 500 g flour, 350 g water and 100 g of 100% hydration starter is 72.73% hydration, not 70%. This is a calculation example, not a tested bread recipe.
Split the starter first
Starter hydration describes the water relative to flour in the starter itself. At 100%, a 100 g starter contains 50 g flour and 50 g water. For any hydration H, starter flour = starter weight ÷ (1 + H/100). Starter water = starter weight minus starter flour. Enter the hydration of the starter you actually use; a feeding ratio alone does not always establish it.
Check the example
Add 50 g starter flour to 500 g recipe flour: total flour is 550 g. Add 50 g starter water to 350 g recipe water: total water is 400 g. Then 400 ÷ 550 × 100 = 72.73%. Salt is not part of either side of this fraction. In the calculator, enter added flour and added water separately from starter to avoid counting it twice.
What changes with a stiff starter?
If the same 100 g starter is at 50% hydration, it contains about 66.67 g flour and 33.33 g water. Keeping the added flour and water unchanged gives 383.33 ÷ 566.67 × 100 = 67.65%. Starter weight alone therefore cannot tell you the final hydration.
Use the result carefully
Weigh ingredients in grams and keep full precision until the final result. Starter percentage and hydration are different measurements: one describes how much starter you add, the other describes the water-to-flour ratio. This calculator models flour, water, starter and salt; milk, eggs, fruit and other additions need separate ingredient accounting. The percentage helps compare formulas, but does not predict fermentation time or guarantee a particular crumb.