Sourdough Starter Feeding Ratio Calculator (1:1:1, 1:2:2, 1:5:5)
A feeding ratio such as 1:2:2 means 1 part starter : 2 parts flour : 2 parts water, by weight. 20 g of starter fed 40 g flour and 40 g water is a 1:2:2 feed. The ratio sets how much fresh flour the starter gets, and the flour-to-water part sets the starter's hydration.
The math
Add up the parts, divide what you need by that total, and multiply back:
one part = (starter needed + extra to keep) ÷ (starter part + flour part + water part)
Then starter = one part × starter part, flour = one part × flour part, water = one part × water part.
Worked examples
| You need | Ratio | Parts total | Starter | Flour | Water |
|---|---|---|---|---|---|
| 100 g | 1:1:1 | 3 | 33.3 g | 33.3 g | 33.3 g |
| 100 g | 1:2:2 | 5 | 20 g | 40 g | 40 g |
| 100 g | 1:5:5 | 11 | 9.1 g | 45.5 g | 45.5 g |
| 150 g (100 g + 50 g to keep) | 1:2:2 | 5 | 30 g | 60 g | 60 g |
| 100 g | 1:2:1.5 | 4.5 | 22.2 g | 44.4 g | 33.3 g |
The last row feeds less water than flour, so the fresh part is at 75% hydration: a stiffer starter.
What the ratio changes
- How much fresh flour per gram of starter. At 1:1:1 the starter gets its own weight in flour; at 1:5:5 it gets five times its weight.
- Hydration. Equal flour and water parts (like 2:2) keep the starter at 100% hydration. The hydration calculator shows how that carries into the dough.
How long your starter takes to peak at a given ratio is something to measure in your own kitchen: note the time from feeding to peak and the room temperature. The schedule calculator can then scale that time to a warmer or cooler day.
Sources
- Arithmetic of the ratio (parts by weight). All numbers above are computed with it.