Sourdough Starter Feeding Calculator
Calculate sourdough starter feeding ratios and build any amount for a recipe.
Returns seed, flour and water in grams with a temperature-adjusted peak time.
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
Hydration is the water weight as a percentage of the flour weight. A 100% hydration starter is equal parts flour and water and is what most recipes assume, so that is the default here. Set the hydration field to something else and the water moves while the flour stays put:
Water_to_Add = Seed_Starter × R × (Hydration / 100)
A stiff starter at 65% ferments more slowly and tastes more acetic, which is what you want for a panettone or a long cold retard. A liquid starter at 125% goes sour faster and is easier to pour but peaks and collapses in a narrower window, so it is less forgiving if you cannot get to it on time. Below about 60% it stops behaving like a batter at all and you are effectively feeding a dough.
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.
The peak times in the ratio table are all quoted at 24°C. Enter your actual kitchen temperature and the calculator shifts them, which matters more than people expect: the same 1:3:3 feed that is ready before breakfast in August is still slack at lunchtime in January.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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