Sourdough Starter Feeding Ratio Calculator
Work out the flour and water to add when feeding a sourdough starter at a chosen ratio, plus the resulting weight and hydration.
How it works
Flour to add = kept starter × flour part · Water to add = kept starter × water part · Ratio = starter : flour : water
A feeding ratio like 1:2:2 means for each part of existing starter you add two parts flour and two parts water by weight. A larger ratio dilutes the microbes into more fresh food, so the starter takes longer to peak — useful for overnight feeds or warm kitchens — while 1:1:1 peaks fast and suits same-day baking. When flour and water parts are equal, the fresh feed is at 100% hydration; keeping a 100%-hydration starter means the whole culture stays at 100% too.
Worked example
You keep 50 g of starter and feed it 1:2:2. You add 50 × 2 = 100 g flour and 50 × 2 = 100 g water, giving 50 + 100 + 100 = 250 g of starter at 100% hydration, ready to peak in a few hours.
Frequently asked questions
What does a 1:5:5 feed do?
It dilutes your starter heavily into fresh flour and water, slowing fermentation so the culture peaks many hours later. That is ideal for feeding before bed or in a warm room where a small feed would overshoot quickly.
How much starter should I keep back?
Only what you need. Many bakers keep just 20–50 g between bakes to reduce flour waste, then scale up with a larger feed a day or two before baking.
Does the ratio change the hydration?
Not if you add equal parts flour and water — the starter stays at 100% hydration regardless of the ratio size. Hydration only changes if the flour and water parts differ, e.g. a 1:2:1 feed makes a stiffer starter.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.