What to weigh, and when it peaks.
A sourdough starter calculator. Say how much ripe starter you need and how you want to feed it.
Your feed
Peaks in about
0 h
fed → peak
Weigh out
Starter0 g
Flour0 g
Water0 g
Makes 0 g. Scaled up so you never weigh less than 10 g of starter.
How it is worked out
A tenth extra
The amounts include a tenth more than you asked for, for what sticks to the jar and the spoon.
More food, more time
Time to peak grows with the square root of the food: four times the food takes about twice as long.
Warm is fast
Fermentation roughly doubles in speed for every 10°C. A warm kitchen shortens the wait and a cool one stretches it.
This is an estimate from one number about your starter. The app does the same sum from your own feedings and corrects itself each time you tell it the jar has peaked.
Which feeding ratio should I use?Glossary
Updated 7 October 2026