Sourdough Starter Feeding Calculator
Work out exactly how much starter, flour and water to use at each feed. Enter the total starter weight you want and your feeding ratio to get a precise feeding plan.
Work Out How Much Flour and Water to Feed Your Starter
Sourdough Starter Feeding Formula
Where:
- \(T\) — desired total weight of starter after feeding (g or oz)
- \(S\), \(F\), \(W\) — the starter, flour and water parts of the feeding ratio
- \(K\) — weight of existing starter to keep
- \(F_a\), \(W_a\) — fresh flour and water to add
The three ratio parts split the desired total by weight, so the fed starter ends up at exactly the size you asked for. The hydration of the fed starter is then calculated from what the kept starter contributes:
\[ H_{fed} = 100 \times \frac{K \cdot \frac{h}{100+h} + W_a}{K \cdot \frac{100}{100+h} + F_a} \]
where \(h\) is the hydration of the existing starter. A starter kept at 100% hydration contains equal weights of flour and water, so each 100 g of it contributes 50 g flour and 50 g water.
Sourdough Starter Feeding – Calculation Example
Example: you want 300 g of starter after feeding, using the classic 1:1:1 ratio, and your existing starter is at 100% hydration.
\[ K = \frac{300 \cdot 1}{1+1+1} = 100 \text{ g}, \quad F_a = \frac{300 \cdot 1}{3} = 100 \text{ g}, \quad W_a = \frac{300 \cdot 1}{3} = 100 \text{ g} \]
The 100 g of kept starter contributes 50 g flour and 50 g water:
\[ H_{fed} = 100 \times \frac{50 + 100}{50 + 100} = 100\% \]
Result: keep 100 g of existing starter, add 100 g fresh flour and 100 g water. The fed starter is 100 g + 100 g + 100 g = 300 g at 100% hydration.
How to Use the Calculator
- Enter the Desired starter amount — the total weight you want to end up with after feeding — and choose g or oz as the unit.
- Set the three parts of the Feeding Ratio (Starter : Flour : Water). The default 1:1:1 is the standard daily feed; use 1:2:2 or 1:3:3 for longer gaps between feeds.
- Enter the Hydration of existing starter as a percentage. Equal weights of flour and water in the original starter is 100%.
- Read your Feeding Plan: how much existing starter to keep, how much fresh flour and water to add, and the hydration of the starter after feeding.
- Discard (or set aside for recipes) any starter beyond the amount to keep, then combine the kept starter with the flour and water shown.
What Is Sourdough Starter Feeding?
A sourdough starter is a live culture of wild yeast and lactic acid bacteria in a mixture of flour and water. Feeding means discarding most of it and adding fresh flour and water to the portion you keep. Without regular feeding, the microbes exhaust their food supply, the starter turns overly sour, and its leavening power fades. A healthy, freshly fed starter is what makes bread rise without commercial yeast.
Bakers describe a feed with a ratio such as 1:1:1 or 1:5:5 — the weight of starter kept compared to the weights of flour and water added. A 1:1:1 feed triples the food available and is typically ready to use in 4 to 8 hours at room temperature. Larger ratios like 1:4:4 dilute the culture more, so the starter takes longer to peak — useful for once-a-day feeds or for building starter overnight for a morning bake.
The other key concept is hydration: water weight divided by flour weight, expressed as a percentage. A 100% hydration starter, made from equal weights of flour and water, is stiff enough to hold structure but loose enough to expand — it is what most recipes assume. If you switch to a stiffer (lower hydration) or runnier (higher hydration) starter, dough hydration changes too, which is why the calculator reports the hydration of the fed starter so you can keep it consistent.
The calculator works entirely by weight. This is deliberate: flour volume varies hugely with scooping and settling, while weights are exact and repeatable. If you are not yet baking with a scale, this is the single tool that will most improve your sourdough consistency.
Ratios at a Glance
| Ratio (S : F : W) | Typical use | Rough time to peak (room temp.) |
|---|---|---|
| 1 : 1 : 1 | Daily maintenance feed | 4–8 hours |
| 1 : 2 : 2 | Every 12 hours or overnight build | 8–12 hours |
| 1 : 3 : 3 | Once-a-day feeding | 12–16 hours |
| 1 : 5 : 5 | Feeding before refrigerating | Up to 24 hours |
Times depend on temperature, flour and how active the culture is — treat them as guidelines and let the starter's rise and aroma tell you when it's ready.
Assumptions, Limitations and Tips
- Water and starter parts are interchangeable in weight, not volume. Always measure by weight; 100 g of water is not the same as 100 ml of flour by any spoon measure.
- The hydration input describes your existing starter — the one you are keeping a portion of. If you build it with equal weights of flour and water, it is 100%. The fresh flour and water you add are handled separately by the ratio.
- Discard is expected. Keeping every gram of starter means exponential growth; the
Frequently Asked Questions
How do I calculate a sourdough feed by hand without the calculator?
Add up the three parts of your ratio (e.g. 1:1:1 = 3), then divide your desired total starter weight by that sum. Multiply the result by each ratio part to get the amount of starter to keep, flour to add and water to add. For 300 g at 1:1:1: 300 ÷ 3 = 100, so keep 100 g starter, add 100 g flour and 100 g water.
What feeding ratio should I use — 1:1:1, 1:2:2 or 1:5:5?
Use 1:1:1 for a daily maintenance feed at room temperature; it peaks in roughly 4–8 hours. Use 1:2:2 for 12-hour intervals or an overnight build, 1:3:3 or 1:5:5 when you want a longer window before the starter peaks, such as feeding before refrigerating. A larger ratio dilutes the culture, so it takes longer to reach peak activity.
Why did the calculator give me a fed-starter hydration that isn't 100%?
The fed hydration only stays at 100% when your existing starter's hydration matches the water-to-flour ratio of your feed. If your starter is at, say, 80% hydration but you feed 1:1:1 (which adds equal flour and water), the mix shifts toward a higher hydration. To stay at 100%, keep the starter's original hydration at 100% and use a 1:x:x ratio.
Can I feed by volume with cups and spoons instead of weight?
It's strongly discouraged. A cup of flour can weigh anywhere from about 110 to 160 g depending on how it's scooped and settled, so volume feeding makes your ratios and hydration unpredictable. If you must, use 1 cup of flour ≈ 120 g and 1 tablespoon of water ≈ 15 g as rough conversions — but a small digital scale is inexpensive and will fix most sourdough consistency problems.
What should I do with the starter I discard at each feeding?
Discard isn't waste — set it aside for discard recipes like pancakes, crackers, waffles or banana bread, or keep a jar in the fridge and collect discard over several days. Only discard that smells clean and pleasant should be used; discard from a neglected or off-smelling starter belongs in the compost. Fresh discard (within a few days of a feed) works best in recipes.
How do I feed a stiff (low-hydration) starter with this calculator?
Enter your starter's actual hydration in the hydration field — for a stiff 50% hydration starter, type 50, not 100. Then set the water part of the ratio lower than the flour part (e.g. 1:2:1) to keep the fed starter stiff too. The calculator computes the resulting hydration so you can adjust the ratio until you land where you want.
Why is my starter not doubling after feeding even though I follow the ratios?
Ratio math is only half the story — activity depends on temperature, flour quality and the health of the culture. Try keeping the starter at 24–27 °C (75–80 °F), switching part of the feed to whole-grain flour like rye for more nutrients, and using a smaller kept-starter portion (a larger ratio) to give the microbes more food. If it still won't rise after several feeds, it may need a few days of consistent twice-daily feeding to recover.