Feeding a 100% hydration sourdough starter
A sourdough starter is just flour, water and time. The standard home-baker recipe is a 100% hydration starter - equal parts flour and water by weight. Our calculator assumes you're using this kind of starter because it's by far the most common and makes the maths cleaner.
A reliable feed
Keep it simple: 1:1:1 by weight. So if you have 20g of starter, feed it 20g of flour and 20g of water. Stir until smooth, cover loosely, leave at room temperature.
When is it ready to bake with?
At room temperature (~20°C), a well-established starter will roughly double in 4–6 hours after feeding. You want to use it at or just after peak - when it has risen, looks domed and is starting to flatten, with visible bubbles throughout. Drop a small spoonful in water: if it floats, you're good to go.
How much starter to keep on hand
Most home bakers keep 30–60g of starter in a jar. If you bake weekly, store it in the fridge between bakes - pull it out the day before, feed it once or twice at room temperature, and it'll be active by bake time. Discard down to 20g before feeding to keep the jar manageable.