Sourdough Starter Calculator

In short A feeding ratio like 1:2:2 means parts by weight — one part of the starter you keep, two parts flour, two parts water. It is not volume and it is not a percentage, and getting that wrong is the commonest reason a starter behaves unpredictably. This works the arithmetic in both directions: tell it how much starter you are keeping and it gives the feed, or tell it how much you need for a bake and it gives the seed to start from. Everything sums back exactly, because nothing is created or lost in a feed. The ratio is really a timing control. A 1:1:1 feed is ready in a few hours because there is little flour to get through relative to the population of organisms; 1:5:5 can take most of a day at the same temperature. Bakers who feed small ratios and bake in the morning and bakers who feed large ratios overnight are doing the same thing at different speeds. Hydration behaves the way you would expect but more slowly than people assume: the fed starter lands between the seed's hydration and the feed's, and each subsequent feed at the same ratio moves it closer without ever quite arriving. And the one thing no calculator can give you is when to use it. A starter is ready at its peak — risen and just beginning to dome — and that depends on temperature far more than on elapsed hours.