Sourdough Starter Feeding Calculator
Scale any feed ratio — 1:1:1, 1:2:2, or your own — to the exact amount of starter you need, or flip it around to see how much flour and water to add to the starter already in your jar.
The finished weight after feeding — aim a little above what the recipe needs.
What's in the jar now — the calculator adds flour and water in ratio.
Formula & how it works
With ratio parts s : f : w and total parts = s + f + w:
From a target total T: starter = T × s ÷ parts, flour = T × f ÷ parts, water = T × w ÷ parts.
From starter on hand S: one part = S ÷ s, then flour = part × f and water = part × w. Feed hydration = water ÷ flour × 100.
Worked example
Want 300 g of starter at 1:2:2? Five parts total, so 60 g starter, 120 g flour, 120 g water — 100% hydration. Already have 50 g in the jar and want to feed it 1:2:2 instead? Add 100 g flour and 100 g water for 250 g total, same hydration.
Feeding your starter well
The ratio controls timing
The first number is the starter, the other two are the fresh flour and water it's fed. A small feed like 1:1:1 peaks fast because there's lots of active culture relative to fresh food; a big feed like 1:5:5 dilutes the culture and takes much longer to rise. Pick the ratio to match how soon you need it and how warm your kitchen is — warmer rooms and bigger feeds pair well.
Scale to what the recipe needs
Decide the total you want, add a small buffer so you keep some back to continue the culture, then let the ratio split it. Working from a target avoids the common trap of feeding a fixed amount and then coming up short for the dough, or building a huge excess you have to discard.
Hydration and flour type
Equal flour and water is 100% hydration; a stiffer 2:1 flour-to-water feed is 50% and ferments more slowly with a milder, sometimes sweeter flavor. Whole grain and rye drink more water and ferment faster, so if you switch flours expect the timing and feel to shift even at the same ratio.