Sourdough Starter Calculator
Sourdough starter maintenance relies on precise feeding ratios. The ratio of existing starter to flour to water (by weight, not volume) determines how fast the starter ferments and peaks. A stiff starter (low hydration) ferments more slowly and has a more acidic, tangy flavor. A liquid starter (high hydration) ferments faster and has a milder flavor. This calculator lets you choose a feeding ratio (like 1:2:2 or 1:5:5) and a hydration percentage, then enter how much total fed starter you need. It calculates exactly how much existing starter, flour, and water to combine. All amounts are by weight, the only accurate method for bread baking.
Feeding ratio formula
Parts = starter_ratio + flour_ratio + water_ratio
Starter (g) = total_needed * (starter_ratio / parts)
Flour (g) = total_needed * (flour_ratio / parts)
Water (g) = total_needed * (water_ratio / parts)
Hydration is adjusted by modifying the water-to-flour ratio within the feed portion. At 100% hydration, flour and water are equal by weight.
Starter health indicators
- A healthy starter doubles in volume within 4-8 hours of feeding at room temperature.
- It should smell pleasantly sour and yeasty, not like acetone, nail polish remover, or rotting food.
- Pink or orange streaks indicate contamination. Discard and start fresh.
- A layer of grey liquid (hooch) on top is alcohol from hungry yeast. Pour it off or stir it in and feed promptly.
Sourdough starter: frequently asked questions
What is a 1:1:1 sourdough feeding ratio?
A 1:1:1 ratio means 1 part existing starter, 1 part flour, and 1 part water by weight. This is the most common maintenance ratio. For example, 50 g starter + 50 g flour + 50 g water.
What is starter hydration?
Hydration is the ratio of water to flour by weight expressed as a percentage. A 100% hydration starter (equal parts flour and water by weight) is the most common. A 75% hydration starter is stiffer and ferments more slowly.
How much starter do I discard before feeding?
You discard the portion not used in the feeding. If you keep 50 g and feed 1:1:1, you discard all but 50 g of your existing starter before feeding. Discard is used to prevent the starter from growing too large.
How often should I feed my sourdough starter?
At room temperature (70-75 F), feed once every 12-24 hours. In the refrigerator, feed once a week. The starter is ready to use when it has doubled in size and passes the float test (a small spoonful floats in water).
What flour should I use for a sourdough starter?
Unbleached all-purpose or bread flour works well for maintenance. Whole wheat flour accelerates fermentation due to additional nutrients and wild yeast populations. Many bakers use a blend of white and whole wheat for balance.
Official sources
- USDA Agricultural Research Service: FoodData Central.
- FDA: Food Safety Resources.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.