How do I feed my sourdough starter?
Type the starter you keep, or the total fed starter you need, and your feeding ratio S:F:W. The sourdough starter calculator gives the flour and water to add and the fed starter’s hydration.
- Flour to add
- 50 g
Feed 50 g of starter with 50 g flour and 50 g water.
- Water to add
- 50 g
- Starter to keep
- 50 g
- Fed starter
- 150 g
- Fed starter hydration (%)
- 100
Flour to add: 50 g. Feed 50 g of starter with 50 g flour and 50 g water.
How to calculate
Works out the flour and water to feed a sourdough starter at a ratio such as 1:1:1 or 1:5:5, from the starter you keep or the total you need, with the fed starter’s hydration.
Example with the default inputs (Start from Starter kept, Starter kept 50 g, Starter part (S) 1, Flour part (F) 1, Water part (W) 1, Starter hydration 100%): Feed 50 g of starter with 50 g flour and 50 g water.
Method: For a feeding ratio S:F:W by weight: flour = starter × F ÷ S; water = starter × W ÷ S. From a total T: starter = T × S ÷ (S + F + W). Hydration = (starter water + water) ÷ (starter flour + flour) × 100, where the kept starter holds starter ÷ (1 + h) of flour.
- The ratio is by weight. The kept starter is only flour and water, at the hydration you give (100% means equal weights).
Worked examples
Each example is checked against the calculator on every build.
- Start from Starter kept, Starter kept 50 g, Starter part (S) 1, Flour part (F) 1, Water part (W) 1, Starter hydration 100% gives Flour to add 50 g, Water to add 50 g, Fed starter 150 g, Fed starter hydration (%) 100.Source: Wikipedia, Sourdough (a starter is kept alive by regular feedings of flour and water), https://en.wikipedia.org/wiki/Sourdough (retrieved 2026-10-03); Wikipedia, Baker percentage (hydration: water weight as a percent of flour weight), https://en.wikipedia.org/wiki/Baker_percentage (retrieved 2026-10-03)
- Start from Total needed, Total starter needed 220 g, Starter part (S) 1, Flour part (F) 5, Water part (W) 5, Starter hydration 100% gives Starter to keep 20 g, Flour to add 100 g, Water to add 100 g, Fed starter hydration (%) 100.Source: Wikipedia, Sourdough (a starter is kept alive by regular feedings of flour and water), https://en.wikipedia.org/wiki/Sourdough (retrieved 2026-10-03); Wikipedia, Baker percentage (hydration: water weight as a percent of flour weight), https://en.wikipedia.org/wiki/Baker_percentage (retrieved 2026-10-03)
- Start from Starter kept, Starter kept 30 g, Starter part (S) 1, Flour part (F) 2, Water part (W) 1, Starter hydration 100% gives Flour to add 60 g, Water to add 30 g, Fed starter hydration (%) 60.Source: Wikipedia, Baker percentage (hydration: water weight as a percent of flour weight), https://en.wikipedia.org/wiki/Baker_percentage (retrieved 2026-10-03)
How it works
A feeding ratio S:F:W gives the weights of starter, flour and water in that order. Each part can be from 0 to 1,000, except S, which is from 0.01 to 1,000.
- From the starter kept: flour = starter × F ÷ S; water = starter × W ÷ S.
- From a total needed T: starter = T × S ÷ (S + F + W), then flour and water as above.
- Fed starter = starter + flour + water.
Hydration. With the kept starter at hydration h (100% by default, under More options), its flour is starter ÷ (1 + h) and its water is that flour × h. The fed starter’s hydration is (starter water + water) ÷ (starter flour + flour) × 100.
Weights convert exactly: 1 oz = 28.349523125 g; 1 lb = 453.59237 g; 1 kg = 1,000 g.
Exact arithmetic. Each value is read as the exact decimal you typed, in its unit, so each weight is an exact fraction until it is rounded for display.
Output format. Weights show in grams to 1 decimal place; the hydration shows as a percent to 1 decimal place.
Assumptions
- The ratio is by weight; the starter is only flour and water.
Worked examples by hand
50 g at 1:1:1. Flour = 50 × 1 ÷ 1 = 50 g; water 50 g; fed starter 150 g; hydration (25 + 50) ÷ (25 + 50) = 100%.
220 g at 1:5:5. Starter = 220 × 1 ÷ 11 = 20 g; flour = 20 × 5 = 100 g; water 100 g.
30 g at 1:2:1. Flour = 60 g; water = 30 g. The kept starter is 15 g flour and 15 g water, so hydration = (15 + 30) ÷ (15 + 60) = 45 ÷ 75 = 60%.
Other questions people ask
What does a 1:1:1 feeding ratio mean?
One part starter, one part flour and one part water, by weight. Feeding 50 g of starter at 1:1:1 means adding 50 g of flour and 50 g of water, for 150 g of fed starter.
How do I get an exact amount of starter for a recipe?
Pick Total needed and type it. The starter you keep is the total × S ÷ (S + F + W). For 220 g at 1:5:5 that is 220 ÷ 11 = 20 g of starter, fed with 100 g of flour and 100 g of water.
Why use a bigger ratio like 1:5:5 or 1:10:10?
More food per gram of starter means it takes longer to peak, which suits a long or warm day or a feeding before bed. A 1:1:1 feed peaks sooner.
What is starter hydration?
The water in the starter as a percent of its flour. Equal weights of flour and water make a 100% starter. Feeding with less water than flour makes a stiffer starter, such as 60% at 1:2:1.
Does the old starter count toward the hydration?
Yes. The kept starter holds its own flour and water. The page adds them to the new flour and water, using the starter hydration under More options.
How is this different from the sourdough calculator?
This page feeds the starter itself. The sourdough calculator builds the whole dough recipe from baker’s percentages, counting the starter’s flour and water.