Sourdough Starter Feeding Calculator
Calculate sourdough starter feeding ratios and amounts to build the exact quantity you need for baking day.
How Sourdough Starter Feeding Is Calculated
A sourdough starter is a living culture of wild yeast and lactic acid bacteria maintained through regular feedings of flour and water. The feeding ratio determines how quickly the starter peaks and how strong it will be for baking.
Feeding Ratio Notation
Ratios are expressed as Starter : Flour : Water by weight. Common ratios:
| Ratio (S:F:W) | Peak Time (24°C) | Best For |
|---|---|---|
| 1:1:1 | 4-6 hours | Quick builds, warm kitchens |
| 1:2:2 | 6-8 hours | Standard maintenance |
| 1:3:3 | 8-10 hours | Overnight builds |
| 1:5:5 | 10-14 hours | Slow builds, warm climates |
| 1:10:10 | 14-20 hours | Very slow, cool storage |
Build-Up Formula
To calculate how much starter to feed in order to have the right amount at bake time:
Starter_Needed = Recipe_Amount × Safety_Margin
The safety margin (typically 1.1 to 1.2) accounts for what sticks to the jar and is lost during transfer.
Working backward from the ratio:
If your ratio is 1:R:R (where R is the flour and water multiplier):
- Seed_Starter = Starter_Needed / (1 + R + R)
- Flour_to_Add = Seed_Starter × R
- Water_to_Add = Seed_Starter × R
Worked Example
You need 200 g of starter for your bread recipe, using a 1:3:3 ratio:
- With safety margin: 200 × 1.15 = 230 g total
- Seed starter: 230 / (1 + 3 + 3) = 230 / 7 = 32.9 g
- Flour: 32.9 × 3 = 98.6 g
- Water: 32.9 × 3 = 98.6 g
- Total: 32.9 + 98.6 + 98.6 = 230.1 g
Hydration Considerations
The calculator assumes 100% hydration (equal parts flour and water by weight), which is the most common. If you need a stiff starter (65% hydration) or a liquid starter (125% hydration), the water amount changes accordingly:
Water_to_Add = Seed_Starter × R × (Hydration / 100)
Temperature and Peak Time
Fermentation speed roughly doubles for every 8°C increase in temperature. At 20°C, a 1:3:3 feed peaks in about 10-12 hours. At 28°C, the same feed peaks in 5-6 hours. Plan your feed timing so the starter is at peak (doubled in volume, domed top) when you mix your dough.