Free Sourdough Starter Ratio calculator with clear step-by-step results.
A feeding ratio describes parts of existing starter to flour to water, so a 1:2:2 feed on 50 grams of starter means 100 grams of flour and 100 of water. The water figure is adjusted for starter hydration, and the surplus line tells you whether the feed produces enough levain for the bake plus what you keep back.
Feed quantities
Flour = starter kept x flour parts; water = starter kept x water parts x hydration
Surplus
Surplus = total after feed - levain needed - starter kept back
Higher flour ratios take longer to peak, which suits a fridge-kept starter or an overnight build. A 1:1:1 feed peaks in a few hours and needs using promptly.
The feed is too small to supply both the levain and the next generation. Either keep back more starter or feed at a larger ratio.