# How do I feed my sourdough starter?

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.

- Page: https://www.acalculator.org/food/sourdough-starter-calculator
- JSON spec: https://www.acalculator.org/food/sourdough-starter-calculator.json
- Version: 2291db9222f8

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| from | Start from | The starter you keep and feed, or the total amount of fed starter you need. |
| k | Starter kept | The starter you keep in the jar before feeding. |
| t | Total starter needed | The fed starter you want, for example for a recipe plus some to keep. |
| s | Starter part (S) | The starter part of the feeding ratio S:F:W. |
| f | Flour part (F) | The flour part of the feeding ratio S:F:W. |
| w | Water part (W) | The water part of the feeding ratio S:F:W. |
| h | Starter hydration | The kept starter’s water as a percent of its flour; 100% for equal weights. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| flour | Flour to add | Starter × F ÷ S. |
| water | Water to add | Starter × W ÷ S. |
| starter | Starter to keep | The starter you feed. |
| fed | Fed starter | Starter + flour + water. |
| newHydration | Fed starter hydration (%) | All the water ÷ all the flour × 100, counting the kept starter’s own flour and 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.

## Assumptions

- The ratio is by weight. The kept starter is only flour and water, at the hydration you give (100% means equal weights).

## Worked examples

1. from = keep, k = 0.05, s = 1, f = 1, w = 1, h = 100% gives flour = 0.05, water = 0.05, fed = 0.15, newHydration = 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).
2. from = total, t = 0.22, s = 1, f = 5, w = 5, h = 100% gives starter = 0.02, flour = 0.1, water = 0.1, newHydration = 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).
3. from = keep, k = 0.03, s = 1, f = 2, w = 1, h = 100% gives flour = 0.06, water = 0.03, newHydration = 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).

## FAQ

### 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.

## Sources

- Wikipedia, Sourdough: a starter is kept active by regular feedings of flour and water. Retrieved 2026-10-03. https://en.wikipedia.org/wiki/Sourdough
- Wikipedia, Baker percentage: ingredient weights as a percent of the flour weight; hydration is the water percentage. Retrieved 2026-10-03. https://en.wikipedia.org/wiki/Baker_percentage