Sourdough Starter Calculator — Feeding Ratio and True Hydration

This sourdough starter calculator does two jobs that usually get lumped together, and shouldn’t be.

Use the feeding ratio tool when you are refreshing a starter. Enter the weight of starter you want to feed and a ratio such as 1:2:2 or 1:5:5. The calculator returns the flour and water to add, in grams or ounces.

Use the true hydration tool when you mix a dough. Enter the flour and water in the recipe, the starter you are adding, and the starter’s own hydration (100% is the usual default for a starter kept with equal weights of flour and water). The result is the dough’s real hydration: total water divided by total flour, including the flour and water already inside the starter.

A worked example

Suppose your dough formula is 500 g flour, 350 g water, and 100 g starter at 100% hydration. If you only divide 350 by 500, you get 70%. That figure leaves the starter out.

A 100 g starter at 100% hydration is 50 g flour and 50 g water. The dough actually contains 550 g flour and 400 g water. True hydration is 400 ÷ 550, or 72.7%. The starter has moved the dough a little wetter than the recipe water-to-flour ratio suggests. The more starter you use, or the wetter that starter is, the larger that gap becomes.

The calculator on this page is set up with those numbers so you can change one value and see the hydration move.

How to use it

  1. Choose grams or ounces. Stay in one unit for the whole calculation; you do not need to convert first.

  2. For a feeding, weigh the starter you will keep, pick a ratio (or enter a custom one), and add the flour and water the tool returns.

  3. For a dough, enter the flour and water you are adding, the starter going into the mix, and the starter hydration. Read the true hydration, and the split of flour and water inside the starter, before you decide whether to adjust the water.

The math runs entirely in your browser. Nothing is sent to a server or saved.

Guides

This site is published by Auburnbusiness.com. It is a free tool, not a baking course and not a substitute for your own judgment at the bench.