Make exactly 200 grams
200 g ÷ 5 parts = 40 g per partAt 1:2:2, keep 40 g starter, then add 80 g flour and 80 g water.
← All calculatorsSOURDOUGH STARTER MATH
Sourdough Starter Feeding Calculator
Work backward from the starter you need—or forward from the starter you want to keep—and get exact flour, water, and discard weights.
HOW THE RATIO WORKS
Starter : flour : water, always by weight
A 1:2:2 feed means one part existing starter, two parts fresh flour, and two parts fresh water. The five total parts make it easy to work backward from any finished weight.
Start with 25 grams
25 g × (1 + 2 + 2) = 125 gKeep 25 g starter, then add 50 g flour and 50 g water.
COMMON RATIOS
Compare the math before choosing a feed
| Ratio | Total parts | Seed starter share | Example finished amount |
|---|---|---|---|
| 1:1:1 | 3 | 33.3% | 30 g seed → 90 g total |
| 1:2:2 | 5 | 20% | 30 g seed → 150 g total |
| 1:5:5 | 11 | 9.1% | 30 g seed → 330 g total |
| 1:10:10 | 21 | 4.8% | 10 g seed → 210 g total |
DISCARD WITHOUT GUESSING
Why the calculator asks what is in your jar
In target mode, FermentWise first finds the seed starter required by your ratio. If your jar contains more, the excess is shown as discard. If it contains less, the calculator reports the exact shortage instead of silently producing the wrong ratio.
Discard is removed before feeding. It controls the size of the culture so you do not need exponentially larger amounts of flour and water at every refresh.
COMMON QUESTIONS
Sourdough starter feeding FAQ
What does a 1:2:2 sourdough feeding ratio mean?
The ratio is starter:flour:water by weight. For every 1 gram of starter retained, add 2 grams of flour and 2 grams of water.
How do I calculate a specific amount of sourdough starter?
Add the ratio parts, divide the desired finished weight by that total, then multiply the weight of one part by each ratio number.
How much starter should I discard before feeding?
Keep the seed starter required by your selected ratio and finished amount. The difference between the starter currently in your jar and the amount you keep is the discard.
Is feeding ratio the same as starter hydration?
No. Feeding ratio compares starter, flour, and water. Hydration compares total water with total flour. A 1:2:2 feed maintains a 100% hydration starter when the seed starter is also at 100% hydration.
Can I use ounces instead of grams?
Yes. Ratios work with any weight unit as long as every input uses the same unit. A digital scale is more precise than volume measurements.
Research-based sources
- King Arthur Baking: Testing different sourdough feeding ratios — ratio notation and the effect of feeding ratios.
- University of California Master Food Preservers: Homemade Sourdough Bread Guide — weight-based 1:1:1 feeding example.
- University of Illinois Extension: Sourdough 101 — starter feeding and ratio context.